Problems

Find Top Customers GROUP BYJOINORDER BY SQL Easy 82% 12K Customers From a City SELECTWHEREORDER BY SQL Easy 89% 15K Customers and Their Order Counts JOINGROUP BYAggregation SQL Medium 61% 8.3K Calculate Monthly Revenue GROUP BYDateAggregation SQL Medium 58% 8K Second Highest Salary SubqueryAggregation SQL Medium 47% 9.6K Average Salary by Department GROUP BYAggregation SQL Easy 85% 11K Products Never Ordered SubqueryJOINDISTINCT SQL Medium 63% 7.1K Employees Earning More Than Their Manager Self JoinJOIN SQL Medium 54% 6.8K Top Product Category by Sales JOINGROUP BYAggregation SQL Medium 57% 5.9K Running Total of Revenue Window FunctionsDateAggregation SQL Hard 33% 3.4K Each Customer's First Order Window FunctionsCTE SQL Hard 36% 3.1K Repeat Customer Retention CTEHAVINGAggregation SQL Hard 24% 2.3K List the Product Catalog SELECTORDER BY SQL Easy 75% 7.7K Cities We Serve SELECTDISTINCTORDER BY SQL Easy 89% 9.9K Electronics Price List with Aliases SELECTWHEREORDER BY SQL Easy 77% 9.8K Three Cheapest Products SELECTORDER BYLIMIT SQL Easy 85% 4.9K Line Totals for One Order SELECTWHERE SQL Easy 87% 4.7K Analytics Team Pay Sheet SELECTWHEREORDER BY SQL Easy 79% 4.9K High-Value Orders WHEREORDER BY SQL Easy 74% 4.7K Signups in H2 2023 WHEREDateORDER BY SQL Easy 74% 9.3K Mid-Range Products WHEREORDER BY SQL Easy 73% 6.8K Cancelled or Returned Orders WHEREORDER BY SQL Easy 89% 5K International Customers WHEREORDER BY SQL Easy 72% 7.1K Find the Desk Products WHEREString SQL Easy 74% 9K Five Newest Customers ORDER BYLIMIT SQL Easy 81% 5.5K Orders by Status, then Value ORDER BY SQL Easy 81% 7.3K The Founding Five ORDER BYLIMIT SQL Easy 89% 4.7K Catalog by Category and Price ORDER BY SQL Easy 79% 8.9K Order Count by Status GROUP BYAggregation SQL Easy 78% 8.1K Total Spend per Customer ID GROUP BYAggregation SQL Easy 84% 5.7K Payment Method Breakdown GROUP BYAggregation SQL Easy 88% 7K Products per Category GROUP BYAggregation SQL Easy 81% 9.5K Average Order Value by Month GROUP BYDateAggregation SQL Medium 57% 6.1K Department Headcount GROUP BYAggregation SQL Easy 84% 7.3K Units Sold per Product GROUP BYAggregation SQL Easy 82% 8.7K Customers per Country GROUP BYAggregation SQL Easy 74% 9.8K Largest Order per Customer GROUP BYAggregation SQL Easy 80% 6.2K Cities with Multiple Customers GROUP BYHAVING SQL Easy 78% 5.9K Payment Methods Moving Real Money GROUP BYHAVINGAggregation SQL Medium 54% 4.9K Premium Product Categories GROUP BYHAVINGAggregation SQL Medium 59% 4.1K Customers with 3+ Orders GROUP BYHAVING SQL Easy 79% 6.1K Departments Over Budget Threshold GROUP BYHAVINGAggregation SQL Medium 63% 6.4K Orders with Customer Names JOIN SQL Easy 78% 9.8K Order Lines with Product Names JOIN SQL Easy 73% 7.9K Customers Who Never Ordered JOINNULL Handling SQL Medium 51% 5.3K Orders with No Payment Record JOINNULL Handling SQL Medium 58% 5.9K Payments with Order Status JOIN SQL Easy 75% 6.9K Three-Way Order Report JOIN SQL Medium 46% 5.5K Revenue per Product JOINGROUP BYAggregation SQL Medium 63% 8K Orders from UK Customers JOINWHERE SQL Easy 89% 4.9K Customer Pairs in the Same City Self JoinJOIN SQL Hard 29% 6.4K Employees and Their Managers Self JoinJOIN SQL Medium 62% 7.5K Managers by Team Size Self JoinGROUP BY SQL Medium 54% 6.4K Items on Cancelled Orders JOINWHERE SQL Easy 77% 9.1K Delivered Revenue by Country JOINGROUP BYAggregation SQL Medium 55% 5.5K Line Count per Order JOINGROUP BYNULL Handling SQL Medium 55% 3.9K Orders Above the Average SubqueryAggregation SQL Medium 54% 6.2K Most Expensive Product per Category Subquery SQL Medium 51% 4.3K Customers Who Paid via UPI Subquery SQL Medium 50% 5.1K Paid Above Department Average Subquery SQL Medium 55% 5.5K Products Priced Above Average Subquery SQL Easy 86% 9.7K Each Customer's Latest Order Subquery SQL Medium 56% 6.4K Who Buys Electronics? SubqueryJOIN SQL Medium 63% 4.1K Each Order's Share of Revenue SubqueryAggregation SQL Medium 60% 8.1K Never Bought Furniture Subquery SQL Hard 25% 5.5K Monthly Order Volume via CTE CTEDateGROUP BY SQL Easy 88% 8.8K VIP Customers via CTE CTEJOINAggregation SQL Medium 61% 3.1K Salary vs Department Average CTEJOIN SQL Medium 63% 5.6K Average Customer Lifetime Value CTEAggregationBusiness Case SQL Medium 45% 3.5K Generate Numbers 1 to 10 CTE SQL Medium 62% 6.5K Everyone Under Meera CTESelf Join SQL Hard 32% 3.2K Order Size Buckets CTECASE WHENGROUP BY SQL Medium 57% 7.1K Repeat vs One-Time Customers CTECASE WHENBusiness Case SQL Medium 59% 4.9K Company-Wide Salary Rank Window FunctionsRanking SQL Medium 56% 8.1K Salary Rank Within Department Window FunctionsRanking SQL Medium 53% 3.7K Top 2 Earners per Department Window FunctionsCTERanking SQL Hard 37% 6.6K Dense-Rank Order Values Window FunctionsRanking SQL Medium 62% 3.2K Previous Order Amount (LAG) Window Functions SQL Medium 46% 6.2K Days Between Logins Window FunctionsDate SQL Hard 29% 2.5K 3-Order Moving Average Window Functions SQL Hard 36% 1.5K Share of Each Customer's Spend Window Functions SQL Hard 31% 3.6K Top Earner Name per Department Window Functions SQL Medium 52% 8.1K Salary Quartiles with NTILE Window FunctionsRanking SQL Medium 46% 5.2K Cumulative Order Count Window Functions SQL Medium 47% 3.1K Days Between Consecutive Orders Window FunctionsDate SQL Hard 25% 4K Q1 2024 Orders DateWHERE SQL Easy 87% 6.7K Signups by Month DateGROUP BY SQL Easy 74% 9.2K Orders by Day of Week DateGROUP BY SQL Medium 55% 3.9K Days from Signup to First Order DateCTEJOIN SQL Hard 28% 2.1K Active Days per User per Month DateGROUP BY SQL Medium 51% 6.6K Employee Tenure in Years Date SQL Medium 55% 3.6K Weekend Orders DateWHERE SQL Medium 52% 6.4K Names Up, Cities Down String SQL Easy 88% 4.4K Customers with Long Names StringWHERE SQL Easy 89% 4.7K Customer Display Labels String SQL Easy 89% 9.7K Customer Initials String SQL Easy 86% 7.3K Rename a Category Label StringDISTINCT SQL Easy 74% 8.6K Two-Word Product Names StringWHERE SQL Medium 51% 2.6K Formatted Order Codes String SQL Easy 88% 9.8K Label Orders by Size CASE WHEN SQL Easy 78% 4.8K Salary Bands CASE WHEN SQL Easy 85% 6.1K Pivot Order Statuses into Columns CASE WHENPivotAggregation SQL Medium 59% 5.1K Weekend vs Weekday Revenue CASE WHENDateGROUP BY SQL Medium 62% 7.7K Gold, Silver, Bronze Customers CASE WHENCTEBusiness Case SQL Medium 60% 7.5K Category-Based Sale Prices CASE WHEN SQL Medium 60% 7.8K Who Has No Manager? NULL HandlingWHERE SQL Easy 86% 7.5K Fill Missing Manager IDs NULL Handling SQL Easy 74% 6.3K Paid Amount per Order (0 if Unpaid) NULL HandlingJOIN SQL Medium 61% 8.3K Top 3 Spenders, Ranked RankingWindow FunctionsCTE SQL Medium 59% 6.4K Third Highest Salary RankingSubqueryLIMIT SQL Medium 54% 4.7K Products Ranked by Revenue RankingWindow FunctionsJOIN SQL Hard 33% 7.1K Median Employee Salary RankingWindow FunctionsCTE SQL Hard 30% 1.3K Average Order Value by Country Business CaseJOINGROUP BY SQL Medium 46% 5.7K Repeat Purchase Rate Business CaseSubqueryAggregation SQL Hard 34% 7.1K Monthly Cancellation Rate Business CaseCASE WHENDate SQL Hard 34% 5K Revenue Concentration Risk Business CaseCTEAggregation SQL Hard 31% 5.8K Category Revenue Mix Business CaseJOINSubquery SQL Hard 36% 3.2K Users with 3-Day Login Streaks Business CaseWindow FunctionsCTE SQL Hard 25% 3.2K Daily Active Users (DAU) Business CaseDateGROUP BY SQL Medium 50% 4.6K UPI vs Card, Month by Month Business CaseCASE WHENPivot SQL Hard 30% 6.2K Orders Matching a Price List WHEREORDER BY SQL Easy 86% 8.8K Names Starting with A WHEREString SQL Easy 84% 5.2K Catalog Pagination: Page 2 ORDER BYLIMIT SQL Easy 78% 8.1K The 2023 Hiring Class WHEREDate SQL Easy 79% 7K Salary Floor and Ceiling per Department GROUP BYAggregation SQL Easy 88% 8.1K Average Rating per Product GROUP BYAggregation SQL Easy 74% 5.1K Review Volume by Month GROUP BYDate SQL Easy 82% 6.5K Subscriptions per Plan GROUP BYAggregation SQL Easy 75% 8.3K Payments Processed per Month GROUP BYDate SQL Easy 82% 7.7K Products Reviewed More Than Once GROUP BYHAVING SQL Easy 89% 8.8K Products Averaging 4 Stars or Better GROUP BYHAVINGAggregation SQL Medium 56% 8K One-and-Done Customers GROUP BYHAVING SQL Easy 81% 4K Where Is Each Shipment Going? JOIN SQL Easy 84% 4.2K Reviews, Human-Readable JOIN SQL Easy 72% 6.3K Currently Active Subscribers JOINNULL Handling SQL Medium 45% 8.4K Monthly Recurring Revenue by Plan GROUP BYNULL HandlingBusiness Case SQL Medium 48% 2.8K Delivered Orders Missing a Shipment JOINNULL Handling SQL Medium 62% 3.3K Reviews Without a Purchase JOINSubquery SQL Hard 32% 7.1K Products Nobody Has Reviewed JOINNULL Handling SQL Easy 73% 8.5K Transit Time per Shipment DateNULL Handling SQL Medium 58% 2.8K Which Carrier Delivers Fastest? GROUP BYDateAggregation SQL Medium 59% 6.1K Order Fulfilment Timeline JOINDate SQL Easy 85% 7.4K Products Both Sold and Reviewed JOINDISTINCT SQL Medium 51% 7.5K Buyers Who Also Subscribe (INTERSECT) JOINDISTINCT SQL Medium 59% 3.3K Everyone Who Engaged (UNION) JOINDISTINCT SQL Easy 89% 6.1K Subscribers Who Never Ordered (EXCEPT) JOINSubquery SQL Medium 55% 6K Next Order Amount (LEAD) Window Functions SQL Medium 46% 2.7K ROW_NUMBER vs RANK vs DENSE_RANK Window FunctionsRanking SQL Medium 62% 7K Lowest Earner in Each Department Window FunctionsCTERanking SQL Medium 57% 7.1K Running Total of Spend per Customer Window Functions SQL Medium 54% 7.2K Most Recently Hired per Department (LAST_VALUE) Window Functions SQL Hard 36% 4.3K Order Amount vs Customer's Best Order Window Functions SQL Medium 48% 4.5K Rank a Customer's Own Reviews Window FunctionsRanking SQL Medium 60% 6.4K Sum of This and Previous 2 Orders Window Functions SQL Hard 28% 1.7K Salary Percentile Rank Window FunctionsRanking SQL Hard 33% 2.5K Cumulative Distribution of Order Value Window Functions SQL Hard 38% 4.3K Each User's First Login (Window Version) Window FunctionsCTE SQL Medium 45% 6.8K Customer Spend Deciles Window FunctionsCTERanking SQL Hard 25% 4.8K Did This Customer's Ratings Drop? Window FunctionsCASE WHEN SQL Hard 36% 3.7K Best-Seller per Category (Window Version) Window FunctionsJOINCTE SQL Hard 33% 1.6K Fee Change Between a Customer's Plans Window Functions SQL Medium 60% 6.6K Order Sequence Number per Customer Window Functions SQL Easy 82% 5.9K Each Customer's Second Order Window FunctionsCTE SQL Medium 63% 3.5K Salary Spread Within Department Window Functions SQL Medium 45% 7.9K Shipment Sequence per Carrier Window Functions SQL Easy 77% 8.8K Order Value Z-Score Window FunctionsBusiness Case SQL Hard 26% 5.5K Gap to the Next Highest Salary Window Functions SQL Medium 47% 6.6K Order's Share of Its Own Month Window FunctionsDate SQL Hard 38% 2.3K Customers Ordering More Than Average SubqueryCTE SQL Medium 50% 2.9K Employees Paid Above the Overall Average Subquery SQL Easy 75% 5.1K Customers Who Left a Top Rating Subquery SQL Easy 76% 6.5K Customers Who Never Reviewed Anything SubqueryNULL Handling SQL Medium 46% 5.8K Orders That Have Been Paid (EXISTS) Subquery SQL Medium 62% 8.3K Departments With Nobody Over ₹150k Subquery SQL Medium 45% 3.8K The Most-Reviewed Product SubqueryCTE SQL Medium 61% 4K Above This Customer's Own Average Subquery SQL Medium 50% 3.5K Bargain Products Below Category Average Subquery SQL Medium 54% 7.2K Customers Who Churned and Came Back Subquery SQL Hard 28% 5.9K Second Most Expensive Product SubqueryLIMIT SQL Medium 53% 6.5K Orders With the Most Line Items SubqueryCTE SQL Medium 64% 3.3K Carrier Performance Summary CTEDateAggregation SQL Medium 60% 8.3K Chained CTEs: Top 2 Products per Category CTEJOINRanking SQL Hard 25% 2.1K Compare Two Independent CTEs CTE SQL Medium 46% 5.6K Generate a 6-Month Calendar (Recursive CTE) CTEDate SQL Medium 46% 8.3K Subscription Tenure in Months CTEDate SQL Medium 51% 3.8K Flag At-Risk Subscribers CTECASE WHENBusiness Case SQL Hard 28% 4.9K Depth of Each Employee in the Org Chart CTESelf Join SQL Hard 39% 7K Average Rating from Repeat Reviewers Only CTEHAVING SQL Medium 64% 5.2K Orders in the Trailing 90 Days DateWHERE SQL Medium 47% 8.1K Subscription Renewal Month Date SQL Medium 60% 6.3K Which Quarter Was This Order? DateCASE WHEN SQL Medium 50% 5K Days Since Each User's Last Login DateGROUP BY SQL Medium 60% 3.5K Orders Placed on the Last Day of the Month DateWHERE SQL Hard 32% 1.5K Weekly Signup Cohorts DateGROUP BY SQL Medium 64% 3.4K Payment Lag from Order to Payment DateJOIN SQL Medium 62% 8.1K Normalize City Capitalization String SQL Medium 54% 7.7K Product Name Length Buckets StringCASE WHEN SQL Medium 47% 8.2K Mask Customer Names for a Support Ticket String SQL Medium 56% 3.3K Order Codes with Status Suffix StringCASE WHEN SQL Easy 73% 6.7K Generate Username Handles String SQL Medium 53% 2.8K How Many Words in Each Category Name? String SQL Hard 35% 5.5K Label Ratings as Sentiment CASE WHEN SQL Easy 82% 7.2K Numeric Rank of Subscription Plans CASE WHENORDER BY SQL Medium 64% 3.7K Label Shipment Speed CASE WHENDate SQL Medium 60% 8.2K Nested CASE: Customer Value Segment CASE WHENCTE SQL Hard 33% 2.2K Active or Ended, Explicitly NULL HandlingCASE WHEN SQL Easy 78% 7.9K Orders From Customers With Unknown City NULL HandlingJOIN SQL Medium 55% 5.9K Show Delivery Date or a Placeholder NULL Handling SQL Easy 87% 8.2K Guard Against Divide-by-Zero with NULLIF NULL Handling SQL Medium 52% 7.5K Top 3 Rated Products (Min 2 Reviews) RankingHAVINGCTE SQL Hard 27% 1.5K Rank Carriers by Shipment Volume RankingGROUP BY SQL Medium 56% 7.7K Monthly Active Subscribers Business CaseDateCTE SQL Hard 28% 5.2K Churn Rate by Plan Business CaseCASE WHENGROUP BY SQL Hard 27% 1.7K Week-1 Login Retention Business CaseDateSubquery SQL Hard 39% 7.1K Signup-to-Paid Conversion Funnel Business CaseSubquery SQL Hard 24% 6.7K LTV Proxy vs a Fixed Acquisition Cost Business CaseCTECASE WHEN SQL Hard 29% 4.9K Pivot Revenue by Quarter Business CasePivotCASE WHEN SQL Hard 37% 5.3K H1 vs H2 Revenue Comparison Business CaseCASE WHEN SQL Medium 62% 4.5K Longest Login Streak per User Business CaseWindow FunctionsCTE SQL Hard 27% 1.7K Users Inactive for 30+ Days Business CaseDateGROUP BY SQL Medium 50% 3.7K Average Basket Size Business CaseJOINAggregation SQL Medium 46% 8.2K Frequently Bought Together Business CaseSelf JoinGROUP BY SQL Hard 35% 3.6K Revenue from New vs Returning Customers Business CaseWindow FunctionsCASE WHEN SQL Hard 38% 4.7K Products at Stockout Risk Business CaseJOINGROUP BY SQL Medium 54% 5.8K Refund Exposure by Payment Method Business CaseJOINGROUP BY SQL Medium 47% 4.6K Projected Salary After a 10% Raise, Ranked Business CaseRanking SQL Medium 55% 5.3K Category with the Highest Return Rate Business CaseJOINGROUP BY SQL Hard 36% 4.7K First-Time Buyers per Month Business CaseWindow FunctionsDate SQL Hard 30% 5K Average Time from Delivery to Review Business CaseJOINDate SQL Hard 37% 2.2K Department Cost as % of Revenue Business CaseCTE SQL Medium 48% 5.7K High-Value, Low-Frequency Customers Business CaseCTEHAVING SQL Hard 28% 2.8K Week-over-Week Revenue Change Business CaseWindow FunctionsDate SQL Hard 34% 5.1K Employees Hired the Same Year as Their Manager Business CaseSelf Join SQL Medium 53% 5.5K Do the Top 20% of Customers Drive 80% of Revenue? Business CaseWindow FunctionsCTE SQL Hard 34% 1.5K List Every Ticket Subject SELECTORDER BY SQL Easy 89% 7.4K Computed Column: Is Ticket Urgent? SELECT SQL Easy 81% 5.1K Employee Roster, ID Second SELECTORDER BY SQL Easy 87% 4.7K Prices Converted to Paise SELECT SQL Easy 77% 6.6K What Order Statuses Exist? DISTINCTORDER BY SQL Easy 72% 9.9K Which Payment Methods Are Actually Used? DISTINCTORDER BY SQL Easy 84% 8.5K Priorities Seen Among Open Tickets DISTINCTWHERE SQL Easy 79% 5.9K Which Carriers Have We Used? DISTINCTORDER BY SQL Easy 84% 9.5K The Oldest Still-Open Ticket LIMITWHEREORDER BY SQL Easy 75% 10K Top 5 Priciest Orders LIMITORDER BY SQL Easy 75% 8.1K Employee Directory, Page 2 LIMITORDER BY SQL Easy 84% 7.1K The Single Highest-Rated Review (Earliest Tiebreak) LIMITORDER BY SQL Medium 48% 5.7K Tickets by Custom Priority Order ORDER BYCASE WHEN SQL Medium 47% 8.3K Catalog Sorted by Price, then Name ORDER BY SQL Easy 84% 6.6K Shipments, Delivered First ORDER BYNULL Handling SQL Medium 48% 6.9K Longest-Serving Employees First ORDER BY SQL Easy 85% 8.1K Urgent Tickets Still Open WHERE SQL Easy 88% 6K Everything Except Electronics and Furniture WHERE SQL Easy 73% 8.1K Orders Outside the Typical Range WHERE SQL Easy 74% 8.1K Tickets Resolved the Same Day They Opened WHERENULL Handling SQL Medium 57% 5.3K Customers Who've Filed 2+ Tickets GROUP BYHAVING SQL Medium 58% 8.3K Carriers Handling 3+ Shipments GROUP BYHAVING SQL Easy 76% 9.1K Products Generating Over ₹5000 in Total JOINGROUP BYHAVING SQL Medium 63% 8.3K Departments Averaging 2+ Years Tenure GROUP BYHAVINGDate SQL Hard 30% 3.7K Ticket Resolution Report JOIN SQL Easy 74% 5.4K Customers With Both a Ticket and an Order JOINDISTINCT SQL Medium 45% 7.5K Customers Who Never Filed a Ticket JOINNULL Handling SQL Easy 86% 4.5K Four-Table Order Detail Sheet JOIN SQL Hard 30% 6.1K Employees and Their Peers (Same Manager) Self Join SQL Hard 27% 6.9K Skip-Level Managers Self Join SQL Hard 37% 6.8K Same Country, Different City Self Join SQL Medium 50% 4.7K Products Priced Within ₹100 of Each Other Self Join SQL Medium 49% 5.2K Orders That Generated a Support Ticket JOIN SQL Hard 30% 3K Subscribers Who Also Made a Purchase JOINDISTINCT SQL Medium 49% 2.6K Shipment, Carrier and Payment in One Row JOIN SQL Medium 52% 5.1K Cross-Department Salary Twins Self Join SQL Hard 26% 2.5K Products Reviewed by Multiple Different Customers JOINGROUP BYHAVING SQL Medium 57% 4.5K What Was This Customer's Last Order Before the Ticket? JOINSubquery SQL Hard 37% 3.7K Do Subscribers Buy Physical Products Too? JOINBusiness Case SQL Medium 47% 6.8K Closed Tickets Alongside Order Value JOINSubquery SQL Medium 48% 7.5K Orders Verified to Have Exactly One Shipment JOINGROUP BYHAVING SQL Medium 48% 8K The Customer 360 Row JOINBusiness Case SQL Hard 28% 3K Did a Complaint Follow a Bad Review? JOINDate SQL Hard 34% 3.4K Which Carrier Reaches the Most Cities? JOINGROUP BY SQL Hard 24% 1.6K Fastest Ticket Resolutions, Ranked Window FunctionsRankingDate SQL Medium 45% 5.4K Rank Each Customer's Own Tickets by Age Window FunctionsRanking SQL Medium 59% 5.6K Busiest Carrier Each Month Window FunctionsRankingDate SQL Hard 31% 2.4K Order Rank and Spend Percentile Together Window FunctionsRankingCTE SQL Hard 30% 3.6K Salary Decile per Employee Window FunctionsRanking SQL Hard 28% 6.1K Order Amount vs Trailing 3-Order Average Window Functions SQL Hard 36% 3.2K Global Rating Leaderboard (Min 1 Review) Window FunctionsRankingCTE SQL Medium 58% 8.3K Each Customer's Plan History, Numbered Window Functions SQL Medium 58% 7.5K Top 2 Fastest Carriers RankingWindow FunctionsCTE SQL Medium 62% 8.1K Pivot Ticket Counts by Priority PivotCASE WHEN SQL Medium 50% 4.3K Pivot Delivered Revenue by Carrier PivotCASE WHENJOIN SQL Hard 38% 1.7K Pivot Order Counts: First 3 Months of 2024 PivotCASE WHENDate SQL Medium 51% 7.8K Salary Rank Within Hiring Year Window FunctionsRankingDate SQL Hard 37% 1.4K First and Last Order, Same Row Window Functions SQL Hard 25% 6.1K Rank Customers by Ticket Volume RankingCTE SQL Medium 47% 8.3K Pivot Employee Counts by Salary Band PivotCASE WHEN SQL Medium 62% 3.8K Rank Orders Within Their Own Month Window FunctionsRankingDate SQL Hard 29% 3.4K Longest-Open Tickets, Ranked Window FunctionsRankingDate SQL Medium 51% 4.2K Average Ticket Resolution Time Business CaseDateAggregation SQL Medium 54% 5.3K Resolution Time by Priority Business CaseGROUP BYDate SQL Medium 48% 3.5K SLA-Breaching Urgent Tickets Business CaseWHEREDate SQL Medium 53% 7K Support Burden vs Revenue per Customer Business CaseCTE SQL Hard 35% 2.3K Products Never Even Attempted (EXISTS Form) Subquery SQL Medium 51% 7.9K Above Their City's Average Spend SubqueryCTE SQL Hard 25% 5.6K ARPU Among Active Subscribers CTEBusiness Case SQL Medium 46% 4.8K City of the Single Biggest Spender SubqueryCTE SQL Medium 57% 8.4K Subscription-Only Customers CTESubquery SQL Medium 52% 3.5K Inventory Turnover Proxy by Category Business CaseJOINCTE SQL Hard 27% 6.3K Value of the 2024-Q1 Signup Cohort CTEBusiness CaseDate SQL Hard 37% 3.9K First 10 Fibonacci Numbers (Recursive CTE) CTE SQL Medium 59% 2.8K Revenue Lost to Cancellations Business CaseAggregation SQL Medium 64% 4.5K Customers Who Only Ever Give 5 Stars Subquery SQL Hard 24% 2.2K Support Tickets per 10 Orders Business CaseSubquery SQL Medium 62% 8.3K Simulate a Loyalty Discount CTECASE WHENBusiness Case SQL Hard 26% 6.8K Company Headcount Growth Over Time (Recursive) CTEWindow FunctionsBusiness Case SQL Hard 30% 4.7K Basic Subscribers Who Spend Like Premium Customers Business CaseCTEJOIN SQL Hard 29% 1.5K Second Most Common Customer City SubqueryCTE SQL Medium 48% 7.3K Orders With No Successful Payment After 14 Days Business CaseSubqueryDate SQL Hard 28% 3K Management Cost per Direct Report CTESelf JoinBusiness Case SQL Hard 26% 5.9K Basket Value: Subscribers vs Non-Subscribers Business CaseCTECASE WHEN SQL Hard 29% 5.4K Week-over-Week Ticket Volume Trend Business CaseWindow FunctionsDate SQL Hard 37% 6.2K List All Coupons SELECTORDER BY SQL Easy 77% 5.4K Discount as a Decimal Fraction SELECT SQL Easy 82% 6K Convert Monthly Salary Basis to Annual SELECT SQL Easy 83% 4.3K Order Amount Plus Estimated Tax SELECT SQL Easy 72% 9.2K Which Coupons Have Ever Been Redeemed? DISTINCTORDER BY SQL Easy 84% 6.3K Departments That Have a Manager Assigned DISTINCTJOIN SQL Medium 49% 6.2K Which Months Did We Ship In? DISTINCTDate SQL Easy 75% 7.2K Distinct Customer-City Pairs Present DISTINCT SQL Easy 77% 7.9K The Most Recent Coupon Redemption LIMITORDER BY SQL Easy 85% 9.7K Top 3 Highest-Value Shipped Orders LIMITJOINORDER BY SQL Medium 46% 2.6K Support Ticket Queue, First Page LIMITORDER BY SQL Easy 72% 4.2K Coupons Starting with a Season Prefix StringWHERE SQL Easy 76% 5.1K Tickets Mentioning Refunds StringWHERE SQL Easy 86% 8K Last-Letter Initials String SQL Medium 60% 3K Product Names Without Spaces String SQL Medium 50% 4.1K Abbreviate Ticket Priority StringCASE WHEN SQL Medium 55% 2.8K Shortest and Longest City Names StringDISTINCT SQL Medium 64% 8.3K Redemption Count per Coupon GROUP BYAggregation SQL Easy 75% 6.8K Orders and Their Coupon Savings JOIN SQL Medium 50% 4.2K Full-Price Orders (No Coupon Used) JOINNULL Handling SQL Easy 87% 9.6K Coupons Nobody Has Used JOINNULL Handling SQL Easy 76% 8.1K Coupon Misuse: Below the Minimum Order JOINBusiness Case SQL Hard 32% 2.1K Redemptions Outside the Coupon's Valid Window JOINDateBusiness Case SQL Hard 38% 4.6K Total Discount Given, by Month JOINDateGROUP BY SQL Hard 37% 2.2K Overall Coupon Redemption Rate Business CaseSubquery SQL Medium 48% 4.4K Tickets from Currently Active Subscribers JOIN SQL Medium 62% 4.9K Products Bought Only by High Spenders JOINSubqueryBusiness Case SQL Hard 33% 6.1K Employees Hired Before Their Manager (Data Check) Self Join SQL Medium 46% 8.2K Customer Pairs in the Same City, Different Signup Years Self JoinDate SQL Hard 24% 2.8K Carriers Serving the Same Customer Twice JOINGROUP BYHAVING SQL Hard 30% 5.2K Categories Bought by 3+ Distinct Customers JOINGROUP BYHAVING SQL Medium 56% 5.6K Managers With a Team of 3 or More Self JoinHAVING SQL Medium 61% 6K Cities Where Average Customer Spend Exceeds ₹2000 JOINGROUP BYHAVING SQL Hard 34% 1.4K Products with No Rating Below 4 GROUP BYHAVING SQL Medium 53% 8.2K Managers With an Above-Average Team Self JoinHAVINGSubquery SQL Hard 32% 4.7K Customers Who Ordered in Every Quarter of 2024 GROUP BYHAVINGDate SQL Hard 26% 3.3K Customers Whose Orders Used 2+ Different Carriers JOINGROUP BYHAVING SQL Hard 31% 3.7K Salary Values Shared Across Departments GROUP BYHAVINGSelf Join SQL Hard 39% 6.7K Interleaved Orders and Tickets per Customer JOIN SQL Hard 38% 2K Products Bought and Then Reviewed by the Same Order's Buyer JOIN SQL Hard 29% 2.8K Departments With 2+ Employees Above ₹100k GROUP BYHAVING SQL Medium 60% 4.8K Products This Customer Buys Every Single Time Self JoinGROUP BYHAVING SQL Hard 24% 4.7K Customers With Both High and Low Priority Tickets GROUP BYHAVING SQL Hard 31% 1.5K Redemption Order per Coupon Window Functions SQL Medium 57% 8K Days Between a Coupon's Consecutive Uses Window FunctionsDate SQL Hard 24% 6.8K Top 2 Busiest Carriers per Month Window FunctionsRankingCTE SQL Hard 36% 6.1K Salary Rank and Distance from Department Average, Together Window FunctionsRanking SQL Hard 34% 4.5K Pivot Coupon Redemptions by Quarter PivotCASE WHENDate SQL Hard 38% 5.9K Pivot Order Status Counts by Quarter PivotCASE WHENDate SQL Hard 31% 6.7K Rank Tickets by the Filer's Lifetime Value Window FunctionsRankingCTE SQL Hard 25% 5.3K Resolution-Speed Quartiles Window FunctionsRanking SQL Hard 29% 4.8K Each Customer's First-Ever Coupon Used Window FunctionsJOIN SQL Medium 53% 5.3K Rank Products by Rating Within Their Price Tier Window FunctionsRankingCASE WHEN SQL Hard 24% 2.7K Rank Cancelled/Returned Orders by Value RankingWindow Functions SQL Medium 51% 3.3K Pivot Headcount by Tenure Band PivotCASE WHENDate SQL Medium 64% 5.2K Compare Each Order to the Grand Total (No Self-Join) Window Functions SQL Medium 49% 6K Rank Customers by Support-to-Purchase Ratio Window FunctionsRankingCTE SQL Hard 38% 5.6K Coupon ROI: Revenue per Rupee Discounted Business CaseJOINCTE SQL Hard 24% 5K Customers Eligible for FLASH50 Who Never Used It SubqueryBusiness Case SQL Hard 39% 3K Net Revenue After All Discounts CTEBusiness Case SQL Medium 52% 2.8K Departments Larger Than the Company Average SubqueryCTE SQL Medium 52% 3K Value Density: Items per ₹1000 Spent Business CaseJOIN SQL Medium 45% 2.7K Customers Whose Spending Is Declining CTEWindow FunctionsBusiness Case SQL Hard 38% 1.4K How Fast Do Customers Pay After Ordering? Business CaseJOINDate SQL Medium 58% 5.2K Which Category Has the Highest Markup? SubqueryCTEBusiness Case SQL Hard 39% 4.2K Escalation List: High-Value, Unhappy, Vocal CTEBusiness CaseJOIN SQL Hard 26% 5.6K Does a Higher Plan Price Mean Shorter Tenure? Business CaseCTEDate SQL Hard 38% 3.2K Individual Contributors at the Top (Data Anomaly Check) Subquery SQL Medium 60% 4.3K Order Frequency: Subscribers vs Non-Subscribers Business CaseWindow FunctionsCTE SQL Hard 38% 1.9K Full Org Chart with Path CTESelf Join SQL Hard 33% 3.5K Average Discount Depth Across All Redemptions Business CaseJOIN SQL Easy 75% 4.2K Cost-to-Revenue Ratio, Company-Wide CTEBusiness Case SQL Medium 50% 8.5K Most Improved Carrier (H1 vs H2 Speed) SubqueryCTEBusiness Case SQL Hard 36% 3.3K What Share of Orders Led to a Support Ticket? Business CaseSubqueryDate SQL Medium 57% 3.2K Top Spender in Each Country CTEWindow FunctionsJOIN SQL Hard 27% 4.7K Did Coupon Orders Skew Smaller? Business CaseCASE WHENCTE SQL Hard 35% 6.3K Top Earner Flag per Department (Subquery Form) Subquery SQL Medium 61% 6.6K Do Cancelled-Order Customers File More Tickets? Business CaseCTECASE WHEN SQL Hard 31% 6.3K The Longest-Running Active Subscription CTEDate SQL Medium 53% 3.3K Basket Diversity: Gold vs Bronze Customers Business CaseCTECASE WHEN SQL Hard 37% 4.1K Carriers Slower Than the Network Average SubqueryCTE SQL Medium 56% 7.3K Net New Customers per Quarter of 2024 CTEDateBusiness Case SQL Medium 54% 5.8K Do Customers Rate Lower After Filing a Ticket? Business CaseJOINDate SQL Hard 28% 2.5K Do Premium Subscribers Prefer a Different Payment Method? CTEJOINBusiness Case SQL Hard 33% 1.4K Which Day of the Week Gets the Most Tickets? DateGROUP BY SQL Medium 58% 7.2K First 5 Products Alphabetically ORDER BYLIMIT SQL Easy 82% 7.6K Which Years Have We Had Signups? DISTINCTDate SQL Easy 82% 5.9K Full Employee Record, Renamed Columns SELECT SQL Easy 85% 8.9K Pivot: Delivered vs In-Transit Shipment Counts PivotCASE WHEN SQL Easy 85% 6.8K Cheapest Product in Each Category Subquery SQL Easy 89% 7.5K Cities With Exactly One Customer GROUP BYHAVING SQL Easy 73% 8.3K Employees Hired the Same Month (Any Year) Self JoinDate SQL Medium 57% 2.6K Ratings With the Order That Prompted Them JOINSubquery SQL Medium 56% 7.6K Top 3 Most Frequent Ticket Filers LIMITGROUP BYORDER BY SQL Easy 87% 6.5K Coupon Code Lengths String SQL Easy 85% 7.2K Tickets With No Closure Yet NULL HandlingWHERE SQL Easy 74% 9K Classify Orders by Currency Tier CASE WHEN SQL Easy 84% 6.2K Rank Managers by Team Size RankingSelf JoinCTE SQL Medium 55% 6.5K Running Count of Orders Over Time Window Functions SQL Easy 79% 6K Tickets Filed by the Top 3 Spenders SubqueryCTE SQL Medium 60% 7.2K 3-Month Rolling AOV Trend Business CaseWindow FunctionsDate SQL Hard 39% 7.2K Who Used Each Coupon? JOIN SQL Easy 81% 6.1K How Many Distinct Categories Do We Sell? DISTINCTAggregation SQL Easy 81% 5.1K Shipments by Carrier, Fastest First, Undelivered Last ORDER BYNULL Handling SQL Medium 64% 2.9K Categories Spanning a Wide Price Range GROUP BYHAVING SQL Medium 56% 7K What Share of Orders Even Qualify for a Coupon? Business CaseSubquery SQL Medium 63% 6.7K Time Until This Customer's Next Ticket Window FunctionsDate SQL Medium 63% 2.6K Rank Coupons by Total Discount Cost RankingJOINCTE SQL Medium 46% 6.6K Rough NPS Proxy from Ratings Business CaseCASE WHEN SQL Medium 56% 4.6K Which Coupons Are Valid Right Now? WHEREDate SQL Easy 83% 9.9K Top 10% of Earners Company-Wide RankingWindow Functions SQL Medium 48% 4.5K Identify the Type Variables & Data Typestype() Python Easy 75% 4.4K Safe String to Integer Variables & Data Typestype casting Python Easy 89% 4.7K List vs Tuple Mutability Variables & Data Typesmutability Python Easy 80% 7.4K Same Object or Just Equal? Variables & Data Typesidentity vs equality Python Medium 46% 7.6K Unpack and Swap Variables & Data Typesmultiple assignment Python Easy 82% 5.9K Truthy or Falsy? Variables & Data Typesboolean coercion Python Easy 82% 7.1K Chained Comparison Check Variables & Data Typeschained comparisons Python Medium 62% 7.2K Augmented Balance Update Variables & Data Typesaugmented assignment Python Easy 89% 4.8K Constant Naming Audit Variables & Data Typesnaming conventions Python Easy 75% 9.1K None or Default Variables & Data TypesNone handling Python Easy 74% 8.2K Format Currency with F-Strings Variables & Data Typesf-strings Python Easy 77% 9.2K Binary, Hex and Octal Literal Reader Variables & Data Typesnumber bases Python Medium 60% 3K Complex Number Magnitude Variables & Data Typescomplex numbers Python Medium 46% 4.6K The Float Precision Trap Variables & Data Typesfloating point Python Medium 62% 5.1K Deep Copy vs Shallow Copy Variables & Data Typescopying Python Hard 31% 3.2K Variable Scope Leak Variables & Data Typesscope Python Hard 37% 4.1K Type Coercion in Concatenation Variables & Data Typestype casting Python Medium 49% 4.5K Set vs List: Deduping Without Losing Order Variables & Data Typessets vs lists Python Medium 55% 4.9K Unpacking a Multi-Value Return Variables & Data Typestuple unpacking Python Easy 73% 4.1K Validate and Convert Age Input Input & Outputinput validation Python Medium 50% 2.7K Dict Key Existence vs Falsy Value Variables & Data Typesdictionaries Python Hard 25% 6.4K Greet the User Input & Outputprint() Python Easy 85% 9.9K Custom Separators and End Characters Input & Outputprint() arguments Python Easy 89% 5.7K Parse a CSV Input Line Input & Outputparsing user input Python Medium 45% 6.8K Read Multiple Numbers from One Line Input & Outputparsing user input Python Easy 82% 5.5K Format a Fixed-Width Table Row Input & Outputstring formatting Python Medium 50% 3.9K Echo Lines with Numbers Input & Outputstring formatting Python Easy 76% 6.7K Safe Division with a User-Friendly Message Input & Outputerror output Python Medium 49% 7.8K Build a Text Progress Bar Input & Outputstring building Python Medium 53% 2.9K Mask Sensitive Output Input & Outputstring slicing Python Easy 77% 8.6K Summarize Multi-Line Input Input & Outputaggregating text Python Medium 47% 5.8K Fill a Message Template Input & Outputstring formatting Python Easy 82% 8.2K Validate a Menu Choice from Input Input & Outputinput validation Python Medium 57% 7.7K Redact and Format a Log Line Input & Outputstring processing Python Hard 26% 2.1K Wrap Text to a Fixed Width Input & Outputtext wrapping Python Hard 25% 6.2K Floor Division vs True Division Operatorsarithmetic operators Python Easy 79% 7.9K Modulo for Cyclic Indexing Operatorsmodulo Python Easy 83% 8K Power Operator and Perfect Squares Operatorsexponentiation Python Easy 78% 4.1K Loan Eligibility with Logical Operators Operatorslogical operators Python Medium 60% 8.2K Short-Circuit Evaluation for Safe Lookup Operatorsshort-circuit evaluation Python Medium 58% 5.2K Bitwise Flags for Permissions Operatorsbitwise operators Python Hard 26% 1.6K Bit Shifts for Fast Powers of Two Operatorsbitwise shift Python Medium 58% 3.1K Membership Operator Blocklist Check Operatorsmembership operators Python Easy 77% 9.1K Identity Operator for Cache Hits Operatorsidentity operators Python Medium 64% 4.7K Ternary Operator for Pass/Fail Grading Operatorsconditional expressions Python Easy 86% 9.1K Operator Precedence Puzzle Operatorsoperator precedence Python Medium 49% 3.2K Walrus Operator While Filtering Operatorsassignment expressions Python Hard 28% 5.8K Comparison Operators for Grade Bands Operatorscomparison operators Python Medium 49% 6.8K XOR to Toggle Boolean Flags Operatorsbitwise XOR Python Hard 24% 4.2K Combined Operators: Discount Calculator Operatorsmixed operatorsBusiness Logic Python Medium 51% 4.3K Even or Odd Classifier Conditional Statementsif/else Python Easy 82% 7.5K Positive, Negative, or Zero Conditional Statementsif/elif/else Python Easy 83% 5.7K Leap Year Checker Conditional Statementsnested conditionals Python Easy 82% 8.3K Largest of Three Numbers Conditional Statementsnested conditionals Python Easy 79% 4.1K Exam Grade Bucketer Conditional Statementsif/elif/else Python Easy 75% 5.8K Voting Eligibility Check Conditional Statementsif/else Python Easy 72% 9.8K Triangle Validity Checker Conditional Statementsif/else Python Easy 73% 4K Ternary Rewrite: Absolute Value Conditional Statementsternary operator Python Easy 85% 4.4K Vowel or Consonant Conditional Statementsmembership check Python Easy 75% 5K Season From Month Number Conditional Statementschained comparisons Python Easy 73% 9K Password Strength Checker Conditional Statementsguard clauses Python Medium 60% 7.9K BMI Category Classifier Conditional Statementsif/elif/else Python Medium 54% 6.8K Shipping Fee Tiers Conditional StatementsBusiness Logic Python Medium 56% 7.7K In-Range Check With Chained Comparisons Conditional Statementschained comparisons Python Medium 51% 8.1K Nested If Decision Tree: Loan Eligibility Conditional Statementsnested conditionalsBusiness Logic Python Medium 51% 7K Day of Week From Number With Weekend Flag Conditional Statementsif/elif/else Python Medium 51% 7K Loyalty Discount Tier Calculator Conditional StatementsBusiness Logic Python Medium 45% 7K Rock Paper Scissors Winner Conditional Statementsnested conditionals Python Medium 49% 7.4K Guard Clauses: Validate User Registration Conditional Statementsguard clauses Python Medium 59% 4.3K Truthy/Falsy Branching: Config Defaults Conditional Statementstruthy/falsy Python Medium 61% 3.5K Triangle Type Classifier Conditional Statementsnested conditionals Python Hard 39% 4.4K Progressive Tax Bracket Calculator Conditional StatementsBusiness Logicnested conditionals Python Hard 35% 4.9K Multi-Criteria Employee Bonus Eligibility Conditional StatementsBusiness Logicnested conditionals Python Hard 24% 6.9K Traffic Light State Machine (match-case) Conditional Statementsmatch-case Python Hard 36% 4.2K Simple Command Parser (match-case) Conditional Statementsmatch-case Python Hard 28% 6K Sum of First N Natural Numbers Loopsfor loopaccumulator Python Easy 88% 6.3K Factorial Using a Loop Loopsfor loopaccumulator Python Easy 77% 8.9K Print a Multiplication Table Loopsfor looppattern printing Python Easy 79% 8.5K Count Vowels in a String Loopsfor loop Python Easy 83% 7.4K Reverse a String Using a Loop Loopsfor loop Python Easy 78% 5.7K Find Maximum in a List Using a Loop Loopsfor loop Python Easy 88% 4.8K Print Even Numbers in a Range Loopsrange() Python Easy 79% 5.1K Sum of Digits of a Number Loopswhile loop Python Easy 83% 4.9K Print a Simple Number Triangle Pattern Loopsnested loopspattern printing Python Easy 73% 6.8K Countdown Timer Using a While Loop Loopswhile loop Python Easy 76% 9.6K Enumerate a List With Index and Value Loopsenumerate() Python Easy 74% 5.8K Zip Two Lists Into Pairs Loopszip() Python Easy 89% 6K Repeat String N Times Using a Loop Loopsfor loop Python Easy 82% 6.7K Check Palindrome Using a Loop Loopswhile loop Python Easy 74% 7.7K Prime Number Checker Using a Loop Loopsfor looploop-else Python Medium 55% 4.3K Fibonacci Sequence via Loop Loopsfor loopaccumulator Python Medium 61% 4.9K Nested Loop Multiplication Grid Loopsnested loops Python Medium 51% 3.2K Print a Right-Angled Star Pyramid Loopsnested loopspattern printing Python Medium 57% 6.9K Loop-Else: Search for a Target Value Loopsloop-elsefor loop Python Medium 64% 5.2K Break/Continue Puzzle: Skip Multiples Loopsbreak/continue Python Medium 62% 2.8K Count Frequency of Each Character Loopsfor loopaccumulator Python Medium 55% 7.6K While Loop Input Validation Simulator Loopswhile loop Python Medium 48% 3K Sum of Even and Odd Numbers Separately Loopsfor loopaccumulator Python Medium 64% 5.9K GCD Using a While Loop Loopswhile loop Python Medium 55% 4.3K Print a Diamond Pattern With Nested Loops Loopsnested loopspattern printing Python Medium 64% 5.1K Digit Reversal and Palindrome Number Check Loopswhile loop Python Medium 63% 6.7K Shift Schedule Rotation Printer Loopsfor loopBusiness Logic Python Medium 55% 3.5K Running Total With Threshold Stop Loopswhile loopbreak Python Medium 52% 5.9K Pascal's Triangle Using Nested Loops Loopsnested loopsaccumulator Python Hard 32% 6.5K Prime Numbers Up to N (Sieve With Loops) Loopsnested loops Python Hard 32% 6.8K Matrix Transpose Using Nested Loops Loopsnested loops Python Hard 33% 5.2K Spiral Number Grid Printer Loopsnested loopswhile loop Python Hard 35% 5K Collatz Sequence Length Counter Loopswhile loop Python Hard 39% 4.8K Number Pattern: Floyd's Triangle Variant Loopsnested loopspattern printing Python Hard 38% 7K Perfect Number Finder in a Range Loopsnested loops Python Hard 34% 3.4K Greet With a Default Greeting Functionsdefault arguments Python Easy 86% 9.1K Rectangle Area and Perimeter Together Functionsmultiple return values Python Easy 77% 6.8K Sum Any Number of Scores Functions*args Python Easy 82% 8K Build a User Profile From Keyword Arguments Functions**kwargs Python Easy 85% 9.7K Order Summary With Mixed Arguments Functions*args and **kwargs Python Medium 50% 6K Keyword-Only Shipping Quote Functionskeyword-only arguments Python Medium 51% 7.8K Average of a Variable Number of Numbers Functions*args Python Easy 83% 9.3K Counter Factory Using a Closure Functionsclosures Python Hard 31% 4.2K Global Request Counter Functionsglobal keyword Python Medium 49% 5.3K Apply a Discount Strategy Function Functionsfirst-class functions Python Medium 53% 3.5K Operation Dispatch Table Functionsfunctions in a dict Python Medium 50% 5K Fix the Mutable Default Argument Bug Functionsmutable default arguments Python Medium 46% 6.5K Power Function With Type Hints Functionstype hints Python Easy 84% 6K Temperature Converter With a Proper Docstring Functionsdocstrings Python Easy 73% 8.8K Unpack Coordinates Into a Distance Function Functionsargument unpacking Python Medium 61% 4.2K Validate a Positive Integer Input Functionsinput validation Python Easy 76% 5.2K Curry-Lite: A Function That Returns an Adder Functionsclosures Python Hard 25% 1.3K Check Whether a String Is a Palindrome Functionsreturn values Python Easy 78% 7.1K Apply a Function N Times Functionshigher-order functions Python Medium 46% 5.1K Compose Two Functions Functionsfirst-class functions Python Medium 60% 7.7K Local Variable Shadowing a Global One Functionsvariable scope Python Medium 51% 7.9K Positional-Only Parameters for a Fast Path Functionspositional-only parameters Python Medium 47% 7.3K Retry Wrapper Built by Hand Functionshigher-order functionsclosures Python Hard 33% 2.9K Pure Function to Total a Cart (No Side Effects) Functionspure functions Python Easy 85% 7.9K Impure Function That Logs to a Shared List Functionspure vs impure functions Python Easy 77% 8.4K Grade Classifier With Multiple Return Points Functionsreturn values Python Easy 77% 5.9K Password Strength Checker with Keyword Rules Functionsinput validation Python Medium 47% 3.3K Nested Helper Function for Tax Brackets Functionsnested functions Python Medium 48% 5.8K Function Registry for a Mini Plugin System Functionsfirst-class functions Python Hard 25% 6.6K Demonstrate Default Arguments Are Evaluated Once Functionsdefault argumentsscope Python Hard 31% 6.6K Safe Divide With a Fallback Value Functionsdefault arguments Python Easy 79% 5.4K Word Frequency Counter Utility Functionsutility functions Python Medium 57% 6.2K Function Factory: Choose an Operation at Creation Time Functionsclosuresfirst-class functions Python Hard 36% 6.8K Rectangle-Or-Square Constructor With Smart Defaults Functionsdefault arguments Python Medium 49% 3.3K Build a Text Transform Pipeline From a List of Functions Functionshigher-order functions Python Hard 26% 4.9K BMI Calculator That Returns Value and Category Functionsmultiple return values Python Easy 73% 5.2K Running Average Tracker With Nonlocal State Functionsnonlocalclosures Python Hard 24% 6.5K Keyword Argument Overriding a Positional Default Functionskeyword arguments Python Easy 79% 4.8K Utility Function: Common Elements Between Two Lists Functionsutility functions Python Easy 88% 5.5K Tiered Loyalty Discount Calculator Functionsdefault arguments Python Medium 58% 5.8K Factorial the Recursive Way RecursionMath Python Easy 88% 7.6K Nth Fibonacci Number, Recursively RecursionMath Python Easy 88% 8.5K Sum of Digits via Recursion RecursionMath Python Easy 76% 7.4K Integer Power Function (Recursive) RecursionMath Python Easy 81% 8.5K Greatest Common Divisor via Euclidean Recursion RecursionMath Python Medium 45% 3.3K Sum a List Recursively RecursionLists Python Easy 85% 9.2K Reverse a String Using Recursion RecursionStrings Python Easy 75% 6.2K Count Paths in a Grid (Recursive) RecursionTree-Like Recursion Python Hard 34% 1.9K Sum 1..N — Accumulator vs Plain Recursion RecursionFunctions Python Medium 49% 6.2K Even/Odd Check via Mutual Recursion RecursionFunctions Python Medium 61% 3.2K Fibonacci with a Memo Dictionary RecursionOptimization Python Hard 34% 3K Binary Search, Recursively RecursionSearching Python Medium 62% 6.3K Flatten an Arbitrarily Nested List RecursionLists Python Medium 57% 3.3K Palindrome Check via Recursion RecursionStrings Python Easy 86% 10K Countdown Timer with a Safe Recursion Base Case RecursionError Handling Python Hard 29% 4.8K Pack and Unpack a Sensor Reading TuplesVariables & Data Types Python Easy 77% 5.2K A Tuple's Shell Is Immutable, Its Contents May Not Be TuplesMutability Python Medium 53% 2.6K Tuple or List? Pick the Right Tool TuplesLists Python Easy 79% 9.8K Employee Records with namedtuple Tuplescollections.namedtuple Python Medium 59% 4.5K Caching Grid Computations with Tuple Keys TuplesDictionaries Python Hard 34% 5.4K Rotate Three Variables in One Line TuplesVariables & Data Types Python Easy 73% 9.4K Split a Full Name and Return Multiple Values TuplesStrings Python Easy 77% 8.9K Slice Fields Out of a Fixed-Width Record Tuple TuplesSlicing Python Easy 74% 5.2K Sort Player Scores by Points TuplesSorting Python Medium 53% 3.9K Sum Distances in a Nested Tuple of Points TuplesNested Data Python Medium 50% 8.5K Build a Padded Tuple with + and * TuplesOperators Python Medium 54% 2.9K Zip Three Parallel Lists into Tuple Records Tupleszip() Python Easy 80% 8.1K Compare Version Numbers as Tuples TuplesComparison Python Medium 54% 3.1K Grab Head, Tail and Middle with Star-Unpacking TuplesUnpacking Python Hard 38% 4.7K Round-Trip Between Tuple, List and Set TuplesSets Python Hard 32% 7K Reverse a String with Slicing StringsSlicing Python Easy 82% 5.1K Palindrome Check via Slicing StringsSlicing Python Easy 84% 7.8K Swap the Case of a Sentence StringsCase Conversion Python Easy 86% 9.6K Capitalize Every Word (Title Case) StringsCase Conversion Python Easy 87% 6.1K Trim Whitespace Three Ways StringsWhitespace Handling Python Easy 79% 8.3K Split and Rejoin a Sentence Stringssplit/join Python Easy 85% 5.7K Count Substring Occurrences StringsSubstring Search Python Easy 88% 7K Find and Replace a Word Stringsreplace Python Easy 85% 6.2K Locate a Substring's Position StringsSubstring Search Python Easy 76% 4.8K Filename Extension Checker Stringsstartswith/endswith Python Easy 85% 6.3K Repeat a Character to Build a Border StringsRepetition Python Easy 85% 6.3K Count Words in a Sentence Stringssplit Python Easy 85% 6K Find the Longest Word Stringssplit Python Easy 85% 9.8K Check If a String Is Pure ASCII StringsEncoding Basics Python Easy 78% 8K Extract Substrings with Slicing Tricks StringsSlicing Python Easy 85% 9.4K Tally Vowels and Consonants Separately StringsCharacter Frequency Python Easy 82% 6.7K Add Thousand Separators to a Number String StringsString Building Python Easy 75% 7K Prove Strings Are Immutable StringsImmutability Python Easy 87% 5.6K Anagram Checker StringsAnagrams Python Medium 52% 8.3K Most Frequent Character StringsCharacter Frequency Python Medium 45% 3K Build an Invoice Line with f-strings StringsString Formatting Python Medium 58% 7K Old-Style % String Formatting StringsString Formatting Python Medium 60% 3.4K Align and Pad Columns with format() StringsString Formatting Python Medium 54% 4.9K Build a Large String Efficiently StringsString Building Python Medium 49% 6.5K Normalize Internal Whitespace StringsWhitespace Handling Python Medium 46% 8.3K Manual Substring Search (No find()) StringsSubstring Search Python Medium 52% 3.6K Shift Characters with ord/chr StringsEncoding Basics Python Medium 48% 6.5K String Builder Pattern with a List StringsString Building Python Medium 52% 7K Longest Common Prefix StringsSubstring Search Python Medium 49% 8.2K Run-Length Encode a String StringsString Compression Python Medium 64% 3K Run-Length Decode a String StringsString Compression Python Medium 60% 5.5K Validate a Python Identifier StringsValidation Python Medium 55% 7.2K Fill In Template Placeholders StringsTemplates Python Medium 54% 7.8K Remove Duplicate Characters, Keep Order StringsDeduplication Python Medium 46% 2.5K Strip Unwanted Characters from Input StringsSanitization Python Medium 55% 6K Generate a URL Slug from a Title StringsBusiness Logic Python Medium 54% 5.7K Caesar Cipher Encryption StringsCiphers Python Hard 27% 3.6K Check If One String Is a Rotation of Another StringsSubstring Search Python Hard 35% 5.1K Validate a Username Manually StringsValidation Python Hard 30% 1.3K Parse a Log Line Without Regex StringsParsing Python Hard 39% 1.2K Count Palindromic Substrings StringsPalindromes Python Hard 31% 6.8K Longest Palindromic Substring StringsPalindromes Python Hard 31% 4.1K One Edit Away Check StringsComparison Python Hard 29% 1.5K Group Anagrams StringsAnagrams Python Hard 34% 6.9K First Non-Repeating Character StringsCharacter Frequency Python Hard 39% 6.4K Build a List From a Range ListsCreation Python Easy 88% 4.7K First and Last Element ListsIndexing Python Easy 88% 9K Slice the Middle Section ListsSlicing Python Easy 88% 6.2K Reverse a List With Step Slicing ListsSlicing Python Easy 83% 9.9K Append vs Extend ListsMutation Python Easy 87% 9.2K Insert a Value at a Position ListsMutation Python Easy 73% 6.7K Remove the First Occurrence ListsMutation Python Easy 85% 5.4K Pop an Element and Report Both Parts ListsMutation Python Easy 86% 6.3K sort() In-Place vs sorted() New List ListsSorting Python Easy 82% 5.6K Sort Strings by Length ListsSorting Python Easy 75% 4.6K Sort a List of Tuples by Second Value ListsSorting Python Medium 48% 4.9K Concatenate and Repeat Lists ListsOperators Python Easy 79% 8.8K Flatten a 2D List ListsNested Lists Python Medium 56% 8K Flatten a Deeply Nested List ListsRecursionNested Lists Python Hard 39% 6.2K Min, Max, Sum and Average in One Pass ListsAggregation Python Easy 84% 7.2K Remove Duplicates While Preserving Order ListsDeduplication Python Medium 62% 8.5K Find the Index of a Value ListsSearching Python Easy 82% 4.3K Split a List Into Fixed-Size Chunks ListsSlicing Python Medium 51% 3.4K Rotate a List to the Left ListsSlicing Python Medium 45% 3.7K Rotate a List to the Right ListsSlicing Python Medium 60% 7.3K Zip Two Lists Into Pairs and a Dict ListsZipping Python Easy 86% 7K Merge Two Sorted Leaderboards ListsTwo Pointers Python Hard 24% 1.2K Move All Zeros to the End ListsTwo Pointers Python Medium 64% 3.2K Pair Sum in a Sorted List ListsTwo Pointers Python Medium 47% 8.4K Shallow Copy vs Reference Assignment ListsCopying Python Medium 47% 6.2K List Equality vs Identity ListsIdentity Python Easy 76% 9.7K Transpose a Matrix ListsMatrixNested Lists Python Medium 61% 3.7K Rotate a Matrix 90 Degrees Clockwise ListsMatrixNested Lists Python Hard 35% 3.2K Find the Second Largest Element ListsSearching Python Medium 47% 8K Frequency Count Using Only Lists ListsFrequency Counting Python Medium 61% 7.6K Simulate a Stack With a List ListsStack Python Easy 83% 6K Sum All Numbers in a Nested List ListsRecursionNested Lists Python Medium 48% 5.1K In-Place Doubling vs New List Doubling ListsMutation Python Medium 51% 5.3K Extract a Field From a List of Dicts ListsDicts Python Easy 85% 7.4K Row and Column Sums of a Grid ListsMatrixNested Lists Python Medium 64% 4.1K Insert a Value Into a Sorted List ListsSearching Python Medium 54% 5.8K Common and Unique Elements Between Two Lists ListsComparison Python Medium 64% 3.4K Maximum Sum of a Fixed-Size Window ListsSliding Window Python Hard 38% 2.5K Collapse Consecutive Duplicates ListsDeduplication Python Medium 61% 6.8K Weighted Average From a List of Tuples ListsBusiness Logic Python Medium 61% 2.6K Find the Missing Number in a Range ListsMath Python Medium 59% 4.9K Partition a List Around a Pivot ListsTwo Pointers Python Hard 38% 3K Top N Elements Without Full Sort ListsSelection Python Hard 26% 3K Extract the Boundary of a Matrix ListsMatrixNested Lists Python Medium 64% 5.5K Compare Two Shopping Cart Totals ListsBusiness Logic Python Easy 73% 8.1K Build a Student Record Dictionariescreation Python Easy 80% 9.4K Safe Get with a Default Dictionariesget() Python Easy 81% 7.8K List All Keys and Values Dictionarieskeys()/values() Python Easy 88% 9.5K Check Key Membership Dictionariesmembership Python Easy 79% 8.5K Remove a Key Safely Dictionariespop() Python Easy 85% 7.4K Merge Two Config Dicts Dictionariesmerging Python Easy 75% 7K Nested Address Lookup Dictionariesnested dicts Python Medium 62% 5.4K Word Frequency Counter Dictionariescounting Python Easy 74% 4.8K Invert a Dictionary Dictionariesinversion Python Medium 50% 4.6K Sort a Dict by Value Dictionariessorting Python Medium 64% 7K Group Words by First Letter Dictionariesgrouping Python Medium 52% 4.3K Tally Votes with defaultdict Dictionariesdefaultdict Python Easy 77% 8.5K Most Common Character DictionariesCounter Python Easy 87% 8.8K Iterate and Transform Items Dictionariesiterating items() Python Easy 78% 5.7K Are Two Dicts Equal? Dictionariesequality Python Easy 74% 8.3K Shallow vs Deep Copy of Nested Dicts Dictionariescopying Python Medium 64% 4.1K Build a Dict from Two Parallel Lists Dictionarieszip() Python Easy 76% 7.3K Nested Order Total Traversal Dictionariesnested traversal Python Medium 54% 7.2K Fibonacci with Dict Memoization Dictionariesmemoization Python Medium 54% 5.4K Least Frequent Element Dictionariesfrequency analysis Python Medium 62% 7.6K Key Exists vs Truthy Value Dictionariesexistence vs falsy values Python Easy 83% 9.5K Merge Inventories with Conflict Resolution Dictionariesmergingconflict resolution Python Medium 62% 3.7K Leaderboard Top Scorer Dictionariesleaderboard Python Easy 72% 5.2K Multi-Level Scoreboard Update Dictionariesnested dictsleaderboard Python Hard 29% 3.3K Cache an Expensive Lookup Dictionariescaching Python Medium 56% 3.5K Group Transactions by Category Dictionariesgroupingbusiness logic Python Medium 59% 6.7K First Non-Repeating Character Dictionariesfrequency Python Medium 55% 5.1K Compare Two Inventory Snapshots Dictionariescomparisonbusiness logic Python Hard 30% 3.8K Two Sum Using a Dict Lookup Dictionarieslookup tableclassic Python Medium 55% 7.3K Group Anagrams Dictionariesgroupingstrings Python Hard 29% 6K Update a Deeply Nested Dict Safely Dictionariesnested dictssetdefault Python Hard 39% 4K Find Keys Common to All Dicts Dictionariesset operations Python Medium 47% 6.6K Bucket Support Tickets by Priority Dictionariesbusiness logicgrouping Python Easy 78% 4.3K Coupon Redemption Tally with Cap Check Dictionariesbusiness logicCounter Python Hard 27% 2.4K Symmetric Difference of Two Dicts’ Keys Dictionariesset operations Python Medium 61% 5.7K Deduplicate a Mailing List Setsdeduplication Python Easy 77% 5.9K Safe Tag Manager Setsadd/discard Python Easy 73% 6.7K Skills Both Candidates Share Setsintersection Python Easy 86% 4.8K What Changed Between Two Snapshots Setssymmetric difference Python Medium 50% 8.2K Role Permission Checker Setssubset/superset Python Medium 50% 5.9K Count Unique Meal Combos Setsfrozenset Python Hard 32% 7.1K Find the Missing Invoice IDs Setsdifference Python Medium 59% 8.2K Pangram Detector Setsmembership Python Easy 76% 9.8K No Double-Booked Employees Setsisdisjoint Python Easy 72% 5.1K Customers in Exactly One Campaign Setsset algebra Python Medium 46% 8.1K Merge Watchlists In Place Setsin-place update Python Medium 48% 6.7K Letters Unique to the First Word Setsdifference Python Easy 74% 8.4K First Repeated Product Scan Setsseen-tracking Python Medium 64% 5.7K Drain the Raffle Drum Setspop Python Easy 86% 9.3K Does the Course Cover the Syllabus? Setssuperset Python Medium 59% 8.2K Visitors Active on All Three Days Setsmulti-set intersection Python Medium 59% 6K Fast Stopword Filter Setslookup performance Python Easy 72% 4.5K Detect Duplicate Matchups Setsfrozensetdeduplication Python Hard 30% 2.3K Longest Consecutive Badge Streak Setsalgorithm Python Hard 34% 1.7K Same Inventory, Different Receipts Setsequality Python Easy 82% 6.9K Squares of the Even Numbers List Comprehensionsfilter + map Python Easy 82% 5.2K Pass/Fail Labels in One Line List Comprehensionsconditional expression Python Easy 87% 8.6K Flatten the Seating Chart List Comprehensionsnested loops Python Medium 46% 4.9K Every Size-Color Variant List Comprehensionscartesian product Python Medium 52% 3.8K Build a Price Lookup Dict List Comprehensionsdict comprehension Python Easy 72% 6.3K Distinct Email Domains List Comprehensionsset comprehension Python Easy 88% 5.9K Flag Every Third Row List Comprehensionsenumerate Python Medium 53% 4.1K Apply Per-Item Tax Rates List Comprehensionszip Python Medium 63% 3.8K Clean Up Messy CSV Cells List Comprehensionsstring cleanup Python Medium 57% 3.1K Transpose a Grade Matrix List Comprehensionsnested comprehension Python Hard 39% 2.2K In-Stock Product Names List Comprehensionslist of dicts Python Easy 85% 7.7K Consecutive Reading Pairs List Comprehensionssliding window Python Medium 47% 6.2K Generate Employee Initials List Comprehensionsstring split Python Easy 77% 8.5K Multiplication Table Rows List Comprehensionsnested build Python Easy 84% 5.8K Invert a Country-Code Dict List Comprehensionsdict comprehension Python Medium 54% 6.4K Filter Valid Coupon Codes List Comprehensionsmultiple conditions Python Medium 60% 7.9K Podium Finishers with Medals List Comprehensionszip + slicing Python Medium 49% 7.5K Extract Numeric Ticket IDs List Comprehensionsstring parsing Python Hard 29% 4.4K Heatmap Cell Symbols List Comprehensionsnested conditional expression Python Hard 26% 1.9K Word Length Frequency Report List Comprehensionsdict comprehensionaggregation Python Hard 33% 6.1K Sort Products by Price Lambda & Functionalsorted key Python Easy 74% 6.9K Convert Temperatures with map() Lambda & Functionalmap Python Easy 82% 8.8K Filter Voting-Age Users Lambda & Functionalfilter Python Easy 78% 6.7K Cart Total with reduce() Lambda & Functionalreduce Python Medium 63% 5.6K Best-Rated Restaurant Lambda & Functionalmax with key Python Easy 82% 5.2K Sort by Grade, Then Name Lambda & Functionalmulti-key sort Python Medium 49% 7.8K Element-wise Order Totals Lambda & Functionalmap multiple iterables Python Medium 48% 8K Drop the Failed Sensor Reads Lambda & Functionalfilter None Python Easy 78% 8.1K Peak Traffic via reduce() Lambda & Functionalreduce Python Medium 64% 5K Calculator Dispatch Table Lambda & Functionaldict of lambdas Python Medium 46% 6.3K Fleet Health Checks with any() and all() Lambda & Functionalany/all Python Medium 55% 4.9K Nearest Delivery Hub Lambda & Functionalmin with key Python Medium 49% 8.2K Compose Two Transformations Lambda & Functionalfunction composition Python Hard 24% 5.1K Flatten with reduce() Lambda & Functionalreduce Python Hard 29% 2.9K Preset Shipping Calculators with partial() Lambda & Functionalfunctools.partial Python Hard 24% 5.6K Leaderboard from a Score Dict Lambda & Functionalsorting dict items Python Medium 52% 6.7K Chained map-filter Salary Pipeline Lambda & Functionalmap + filter chain Python Medium 59% 3.9K The Late-Binding Lambda Trap Lambda & Functionalclosureslate binding Python Hard 34% 2.6K Apply a Function over Argument Tuples Lambda & Functionalargument unpacking Python Hard 25% 2.8K Two-Pass Stable Sort Trick Lambda & Functionalstable sort Python Hard 28% 6K Count the Lines in a Log File File Handlingreading Python Easy 78% 5.6K Write a Daily Report File File Handlingwriting Python Easy 72% 7.8K Append to an Audit Trail File Handlingappend mode Python Easy 85% 7.6K Read the Non-Blank Lines File Handlingcleanup Python Easy 78% 9.7K Read a File, or a Default File Handlingexistence check Python Easy 84% 9.5K Total a Sales CSV by Hand File Handlingcsv parsing Python Medium 50% 7.8K Mini-Grep: Matching Lines with Numbers File Handlingsearch Python Medium 48% 3.1K Copy a File Without Comment Lines File Handlingread + write Python Medium 57% 6.1K Implement tail -n File Handlingtail Python Medium 57% 4.5K Most Frequent Word in a Document File Handlingaggregation Python Medium 49% 8.1K Merge Two Sorted Roster Files File Handlingmerging Python Hard 33% 4.6K Checksum a Large File in Chunks File Handlingbinary modechunked reading Python Hard 25% 6.8K Preview, Rewind, Re-read File Handlingseek/tell Python Hard 25% 2.2K Parse a key=value Config File File Handlingparsing Python Medium 54% 7.8K Deduplicate a File In Place File Handlingdedup + rewrite Python Medium 50% 5.7K Text File Statistics File Handlingcounting Python Easy 75% 9.4K Rotate a Log File by Size File Handlingos modulerotation Python Hard 31% 1.3K List All Text Files in a Folder File Handlingos.listdir Python Easy 77% 8.1K Crash-Safe File Update File Handlingatomic write Python Hard 38% 1.6K Add Line Numbers to a Script File Handlingtransform Python Easy 85% 7.2K Division That Never Crashes Exception Handlingtry/except Python Easy 88% 4.1K Robust Integer Parser Exception HandlingValueError Python Easy 81% 5.7K Diagnose the Failure Type Exception Handlingmultiple except Python Medium 48% 2.5K Always Release the Lock Exception Handlingfinally Python Medium 53% 3.5K The Forgotten else of try Exception Handlingtry/else Python Medium 50% 4.4K Raise on Invalid Discount Exception Handlingraise Python Easy 82% 8.9K Design an InsufficientFunds Error Exception Handlingcustom exceptions Python Medium 63% 3.2K Wrap and Chain the Real Cause Exception Handlingraise from Python Hard 32% 4K Retry a Flaky Operation Exception Handlingretry loop Python Hard 30% 3.6K Collect Every Form Error Exception Handlingvalidation aggregation Python Medium 57% 6.3K Why Catch Order Matters Exception Handlingexception hierarchy Python Hard 30% 2.4K Build a with-Statement Timer Exception Handlingcontext managers Python Hard 26% 5.4K Guard Invariants with assert Exception Handlingassert Python Easy 77% 7.2K Best-Effort Cleanup Exception Handlingsuppression Python Medium 45% 6K Log, Then Re-raise Unchanged Exception Handlingbare raise Python Medium 55% 7.5K Keep Asking Until Valid Exception Handlinginput loop Python Medium 48% 7.6K Translate API Error Codes Exception Handlingraising by lookup Python Medium 64% 6.5K Commit or Roll Back Exception Handlingtransaction pattern Python Hard 30% 3.2K Read an Exception Message Safely Exception Handlingexception object Python Easy 80% 5.8K Process What You Can, Report the Rest Exception Handlingpartial failure Python Medium 60% 4K Circle Math with the math Module Modules & Packagesmath Python Easy 78% 6.3K Six-Digit OTP Generator Modules & Packagesrandom Python Easy 79% 4.2K Top-K Items via collections.Counter Modules & Packagescollections Python Easy 87% 8.4K Chunk an Iterable with itertools Modules & Packagesitertools Python Medium 45% 7.6K Portable Path Building Modules & Packagesos.path Python Easy 79% 8.4K Parse Command-Line Arguments Modules & Packagessys.argv Python Medium 57% 4.9K The __main__ Guard, Explained in Code Modules & Packages__name__ Python Easy 82% 6.1K Days Since Signup Modules & Packagesdatetime Python Easy 86% 6.4K Group Employees by Department Modules & Packagescollections.defaultdict Python Medium 53% 5.7K Character Sets from the string Module Modules & Packagesstring module Python Medium 48% 8.3K Import Styles: Module vs from vs as Modules & Packagesimport forms Python Easy 79% 7.2K Grade Summary with the statistics Module Modules & Packagesstatistics Python Easy 73% 5.7K Design a Package Layout Modules & Packagespackage structure Python Medium 51% 5K Three Cheapest Fares with heapq Modules & Packagesheapq Python Medium 61% 7.2K Modules Are Singletons Modules & Packagesimport caching Python Hard 39% 1.2K Model a Library Book OOPclass basics Python Easy 88% 6.3K Store-Wide Tax, Item-Specific Price OOPclass attributes Python Medium 64% 3.5K __str__ vs __repr__ OOPdunder methods Python Medium 53% 3K Encapsulated Bank Account OOPencapsulation Python Medium 61% 6.8K Vehicles That Specialize OOPinheritance Python Easy 72% 4.9K Extend, Don’t Replace, the Constructor OOPsuper() Python Medium 53% 5.8K One Loop, Many Shapes OOPpolymorphism Python Medium 56% 6K Alternate Constructor from a String OOPclassmethod Python Medium 54% 6.5K A Validator That Needs No self OOPstaticmethod Python Easy 81% 5.1K Value Equality for Money OOP__eq__ and __hash__ Python Hard 35% 4.3K Make a Playlist Feel Like a List OOP__len__ and __getitem__ Python Medium 56% 5.6K Overload + for 2D Vectors OOPoperator overloading Python Medium 64% 5K Temperature with a Guarded Setter OOPproperty setter Python Medium 64% 8K Count Your Instances OOPclass state Python Easy 88% 5.3K Force Subclasses to Implement pay() OOPabstract base classes Python Hard 32% 6.6K Invoice as a dataclass OOPdataclasses Python Easy 79% 8.7K An Engine the Car Owns OOPcomposition Python Medium 58% 4.3K Double Underscore Name Mangling OOPname mangling Python Hard 32% 4K Predict the Diamond MRO OOPMROmultiple inheritance Python Hard 28% 4.6K Objects You Can Call OOP__call__ Python Hard 27% 4.5K Support the in Operator OOP__contains__ Python Easy 89% 6.7K Sortable Software Versions OOPcomparison dunders Python Hard 38% 3.2K Lock Down Attributes with __slots__ OOP__slots__ Python Hard 30% 3.9K A Serialization Mixin OOPmixins Python Hard 35% 2.3K isinstance Respects Inheritance, type() Does Not OOPisinstance Python Medium 62% 4.2K A Shopping Cart Object OOPstateful methods Python Easy 82% 6.6K Override AND Reuse the Parent Logic OOPoverride + super Python Medium 55% 5.7K Mini Library Lending System OOPmulti-class design Python Hard 30% 7K Graceful Missing Attributes with __getattr__ OOP__getattr__ Python Hard 29% 2.2K Immutable Coordinates OOPfrozen dataclass Python Medium 46% 6K Swap Pricing Strategies at Runtime OOPstrategy pattern Python Hard 32% 1.2K Duck-Typed Notification Fan-out OOPduck typing Python Medium 45% 5.7K Order Status Observers OOPobserver pattern Python Hard 32% 4.4K Payroll Across a Class Hierarchy OOPinheritance + polymorphism Python Medium 60% 7.7K A Countdown You Can Iterate OOP__iter__ and __next__ Python Medium 56% 7.6K Hand-Rolled vs dataclass Equality OOPdataclass comparison Python Medium 49% 8.4K Singleton via __new__ OOP__new__singleton Python Hard 25% 3.1K Template Method for Reports OOPtemplate method Python Hard 34% 3.5K Deep-Copy an Object Graph OOPcopying objects Python Hard 31% 3K A Door With Legal Transitions Only OOPstate modeling Python Medium 62% 6K Parse an ISO Date String Date & Timestrptime Python Easy 81% 8.9K Format a Date for Humans Date & Timestrftime Python Easy 78% 8.9K Add Business Days to a Date Date & 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Date & Timeinterval logic Python Medium 57% 8K Seconds to H:MM:SS Date & Timeduration formatting Python Easy 75% 5.2K Last Day of Any Month Date & Timecalendar math Python Medium 58% 7.9K Between Epoch and datetime Date & Timeunix timestamps Python Medium 59% 3K Time Remaining, Nicely Worded Date & Timetimedelta breakdown Python Medium 46% 8.4K Logins per Weekday Date & Timeaggregation Python Medium 63% 4.4K Leap Year by the Full Rules Date & Timeleap year Python Easy 72% 9.1K Next Monday After a Date Date & Timeweekday arithmetic Python Medium 60% 7.9K Parse Dates in Mixed Formats Date & Timemulti-format parsing Python Hard 27% 3.8K Show a UTC Time in Another Zone Date & Timetimezones Python Hard 30% 1.8K Current Daily-Login Streak Date & Timestreak logic Python Hard 26% 7K Find All 10-Digit Phone Numbers Regular Expressionsfindall Python Easy 87% 4.7K Practical Email Validator Regular Expressionsfullmatch Python Medium 57% 3.4K Parse Log Lines with Groups Regular Expressionsgroups Python Medium 52% 7.5K Mask Card Numbers in Text Regular Expressionssub Python Medium 50% 3K Split on Any of Several Delimiters Regular Expressionssplit Python Easy 81% 9.2K Extract Hashtags Regular Expressionsfindall Python Easy 83% 5.3K Greedy vs Lazy: Strip Bold Tags Regular Expressionslazy quantifiers Python Hard 31% 4.9K Collapse Runs of Whitespace Regular Expressionssub Python Easy 73% 6.2K Password Rules via Lookaheads Regular Expressionslookaheads Python Hard 28% 6.1K Pull Rupee Amounts from Text Regular Expressionsnumeric capture Python Medium 57% 7.6K Count a Word, Not Its Substrings Regular Expressionsword boundaries Python Medium 46% 8.2K Rewrite Dates with Backreferences Regular Expressionsbackreferences Python Medium 47% 3.5K Compile Once, Scan Many Regular Expressionsre.compile Python Medium 55% 6.4K match vs search vs fullmatch Regular Expressionsmatch/search semantics Python Easy 82% 8.3K Slugify a Blog Title Regular Expressionssub pipeline Python Medium 47% 2.8K Parse a User Profile JSON JSONloads Python Easy 80% 5.9K Pretty-Print Config as JSON JSONdumps options Python Easy 75% 7K Safely Read a Nested JSON Path JSONnested access Python Medium 48% 7.1K Load, Update, Save Settings JSONfile round-trip Python Medium 54% 7.1K Survive Malformed JSON JSONJSONDecodeError Python Easy 88% 5.8K Filter a JSON Array of Orders JSONarray processing Python Medium 63% 8K JSON Types → Python Types JSONtype mapping Python Easy 73% 10K Flatten JSON to Dot-Keys JSONflattening Python Hard 36% 6.9K Serialize Dates with a default Hook JSONcustom serialization Python Hard 27% 6.9K Deep-Merge Two JSON Configs JSONdeep merge Python Hard 30% 4.6K Process a JSON-Lines Stream JSONJSONL Python Medium 63% 5.6K Redact Secrets Before Logging JSONrecursive transform Python Medium 55% 3K CSV Rows to JSON Records JSONformat conversion Python Medium 56% 7.8K Sort a JSON Catalog and Re-serialize JSONparse-sort-dump Python Easy 85% 7.8K Diff Two Flat JSON Objects JSONcomparison Python Hard 24% 1.3K Fetch and Parse a JSON API APIsrequests.get Python Easy 77% 5.8K Send Query Parameters Properly APIsparams Python Easy 85% 9.7K POST a JSON Payload APIspost json Python Easy 73% 9.7K Call a Protected Endpoint APIsauth headers Python Medium 48% 7.6K Never Hang: Timeouts and Fallbacks APIstimeout Python Medium 53% 4.2K Route on Status Codes APIsstatus codes Python Easy 82% 5.1K Walk Every Page of an API APIspagination Python Hard 35% 5.4K Retry with Exponential Backoff APIsretries Python Hard 24% 6.5K Reuse a Session for Many Calls APIsrequests.Session Python Medium 63% 6.1K Stream a Large Download to Disk APIsstreaming Python Hard 39% 3.9K Compose API URLs Without Bugs APIsurl building Python Easy 82% 4.9K Respect Rate-Limit Headers APIsrate limiting Python Hard 33% 3.7K A Testable Weather Client APIsdependency injection Python Medium 62% 3.4K Join Data from Two Endpoints APIsdata joining Python Medium 61% 4.1K Verify a Webhook Signature APIswebhook security Python Hard 34% 5.3K An Endless Fibonacci Stream Iterators & Generatorsinfinite generator Python Easy 72% 7.5K Yield Records in Batches Iterators & Generatorsbatching Python Medium 47% 7.7K Sum a Billion Squares Without a List Iterators & Generatorsgenerator expression Python Easy 76% 5.6K Lazily Yield Numbers from Lines Iterators & Generatorslazy pipeline Python Medium 54% 6.6K Streaming Running Average Iterators & Generatorsstateful stream Python Medium 63% 4.2K The One-Shot Generator Trap Iterators & Generatorsexhaustion Python Medium 58% 8.4K Flatten Deeply with yield from Iterators & Generatorsyield from Python Hard 38% 3.1K Yield the Change Between Readings Iterators & Generatorspairwise Python Medium 62% 4K A Generator You Can send() To Iterators & Generatorssend Python Hard 38% 5.3K Deduplicate an Infinite Stream Iterators & Generatorsstateful filter Python Medium 48% 2.7K Log Every Call Decoratorsbasic decorator Python Easy 77% 9K Time Any Function Decoratorstiming Python Medium 45% 5.5K Hand-Rolled Memoization Decoratorscaching Python Medium 48% 6.7K A Decorator That Takes Arguments Decoratorsdecorator factory Python Hard 33% 5K Reject Negative Arguments at the Door Decoratorsvalidation Python Medium 63% 4.6K Why functools.wraps Matters Decoratorsfunctools.wraps Python Easy 75% 5.8K Role-Gated Endpoints Decoratorsauthorization Python Hard 31% 5K Stacked Decorators Run Bottom-Up Decoratorsstacking order Python Medium 60% 2.8K A Wrapper That Counts Itself Decoratorsfunction attributes Python Medium 63% 5.2K Auto-Register Commands Decoratorsregistry pattern Python Hard 28% 6.3K GST Invoice Calculator Business Logicbilling Python Easy 75% 4.7K Tiered Sales Commission Business Logictiered rates Python Medium 58% 6.5K Loan EMI Calculator Business Logicfinance Python Medium 49% 6.9K Which SKUs Need Reordering? Business Logicinventory Python Easy 79% 7.3K Split a Bill Without Losing Paise Business Logicmoney precision Python Hard 34% 6.8K Ride Surge Pricing Engine Business Logicdynamic pricing Python Medium 58% 5K Loyalty Points with Expiry Business LogicFIFO ledger Python Hard 26% 4.4K Overtime Pay from Punch Logs Business Logicpayroll Python Medium 46% 6.5K Funnel Conversion Report Business Logicmetrics Python Easy 87% 8.1K Train Seats and the Waitlist Business Logicallocation Python Medium 47% 7.8K Price-Drop Alert Trigger Business Logicthresholds Python Easy 82% 4.9K CTC to Take-Home Breakdown Business Logicpayroll Python Medium 58% 2.8K Peak Hour from Reservations Business Logicinterval counting Python Hard 30% 5.4K Refund Eligibility Engine Business Logicpolicy rules Python Medium 51% 5.5K A/B Test Winner (Practical Rule) Business Logicexperimentation Python Medium 45% 3.4K Catch Duplicate Payments Business Logicfraud detection Python Medium 62% 7.5K Pack Orders into Delivery Boxes Business Logicgreedy packing Python Hard 39% 3.4K Prorated Plan Upgrade Business Logicsubscription billing Python Medium 55% 2.9K Compute an NPS Score Business Logicsurvey metrics Python Easy 86% 5.6K Is Every Hour Covered? Business Logiccoverage check Python Medium 48% 8.2K Expense Approval Router Business Logicrouting rules Python Easy 80% 7.3K Month-1 Retention by Cohort Business Logiccohort analysis Python Hard 25% 2K OTP Request Rate Limiter Business Logicrate limiting Python Medium 56% 6.8K Curve Exam Scores to 100 Business Logicnormalization Python Easy 79% 4.3K Book a Room Without Conflicts Business Logicbooking conflicts Python Medium 53% 6.8K Convert Through Cross Rates Business Logicgraph-lite Python Hard 26% 3.6K Flag SLA Breaches Business LogicSLA rules Python Easy 78% 6.2K Feature Flags by Plan Business Logicentitlements Python Easy 89% 4.9K Delivery Partner Weekly Payout Business Logicgig payouts Python Medium 61% 7.8K Reconcile a Stock Ledger Business Logicreconciliation Python Medium 51% 7.5K Happy Hour Discount Windows Business Logictime-based pricing Python Medium 46% 6.1K Score Sales Leads Business Logicscoring Python Medium 53% 2.6K Make Change with Fewest Notes Business Logicgreedy change Python Medium 55% 5.9K Auto-Moderate Product Reviews Business Logicmoderation rules Python Medium 58% 4.6K Electricity Bill by Slabs Business Logicslab billing Python Medium 57% 7.4K Flash Sale Order Processor Business Logicordered allocation Python Hard 25% 6.7K KPI Dashboard Traffic Lights Business Logicdashboards Python Easy 72% 5.6K Merge Duplicate CRM Contacts Business Logicdedup + merge Python Hard 38% 6.1K Project Year-End Revenue Business Logicforecasting Python Easy 77% 4.6K Estimated Wait Time at Support Business Logicqueueing Python Medium 55% 4.9K Which Discounts Stack? Business Logicpromotion rules Python Hard 30% 4.2K