Python data engineering interview problem. Difficulty: advanced. Pattern: Strings. About 20 minutes. Part of the Pro drill bank.
Find the longest substring that reads the same forwards and backwards; the leftmost one on a tie. Treat this as a production helper: match the contracted return shape, including empty and duplicate inputs.
Implement longest_palindrome(s: str) -> str. Return the longest contiguous substring of s that is a palindrome. If several have the same length, return the one that starts earliest. An empty string gives "". The string can have 1,000 characters, so checking every substring one by one is too slow.
Input: longest_palindrome("cbbd") Output: 'bb' The even-length palindrome bb is the longest.
Topics: lakebench, python, palindrome, expand around center.
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Interview-style drill: Find the longest substring that reads the same forwards and backwards; the leftmost one on a tie.
Implement `longest_palindrome(s: str) -> str`. Return the longest contiguous substring of `s` that is a palindrome. If several have the same length, return the one that starts earliest. An empty string gives `""`. The string can have 1,000 characters, so checking every substring one by one is too slow.