Valid Palindrome
Easy · Two Pointers
You are given a string that may contain letters, digits, spaces and punctuation. Keep only the letters and digits, convert them all to lowercase, and check whether the resulting sequence reads the same forwards and backwards. Return true if it does, and false otherwise. An empty resulting sequence counts as a palindrome.
Examples
Input: s = "A man, a plan, a canal: Panama"
Output: true
Why: Ignoring punctuation, spaces and case, the letters read the same forwards and backwards.Input: s = "race a car"
Output: false
Why: Stripped down to letters and digits it becomes 'raceacar', which is not a palindrome.Input: s = " "
Output: true
Why: There are no letters or digits at all, so the empty result trivially reads the same both ways.Constraints
1 <= s.length <= 2*10^5, s consists of printable ASCII characters
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This statement is written for CodeSpeek. The problem is part of the NeetCode 150 list; Watch NeetCode's explanation of Valid Palindrome. Reference solutions from the NeetCode repository (MIT) are used to verify our tests.