Q19: Valid Palindrome. - DSA Patterns (Multi-Lang)

In Simple Words: Two pointers moving towards center. Skip non-alphanumeric characters, compare lowercase characters. If any mismatch, return false; else true when pointers cross.

Time: $O(N)$ | Space: $O(1)$

Multi-Language SolutionsPython 3 • JavaScript • TypeScript • Java • C++

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def isPalindrome(s: str) -> bool:
    l, r = 0, len(s) - 1
    while l < r:
        while l < r and not s[l].isalnum():
            l += 1
        while l < r and not s[r].isalnum():
            r -= 1
        if s[l].lower() != s[r].lower():
            return False
        l += 1
        r -= 1
    return True