longest_common_prefix(strs) that returns the longest string prefix shared by every string in the list strs. If there is no common prefix, or the list is empty, return an empty string.strs = ['flower', 'flow', 'flight']
'fl'
'fl' is the longest prefix common to all three words.
strs = ['dog', 'cat']
''
No shared prefix at all.
Start with the first string as a candidate prefix.
Shrink it one character at a time until every other string starts with it (`str.startswith`).