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Palindrome Checks with Two Pointers

Palindrome Checks with Two Pointers

Two pointers are ideal when you need to compare elements from both ends.

Template for string palindrome checks

def is_palindrome(s):
    left, right = 0, len(s) - 1

    while left < right:
        while left < right and not s[left].isalnum():
            left += 1
        while left < right and not s[right].isalnum():
            right -= 1

        if s[left].lower() != s[right].lower():
            return False

        left += 1
        right -= 1

    return True

Benefits

O(n) time
O(1) additional space
Works well with normalized string comparisons

This exact pattern solves Valid Palindrome.

Practice Problems

Valid Palindrome Easy