0009 - Valid Palindrome

Given a string s, return true if it is a palindrome, otherwise return false.

A palindrome is a string that reads the same forward and backward. It is also case-insensitive and ignores all non-alphanumeric characters.

Example 1:

Input: s = "Was it a car or a cat I saw?"

Output: true Explanation: After considering only alphanumerical characters we have "wasitacaroracatisaw", which is a palindrome.

Example 2:

Input: s = "tab a cat"

Output: false Explanation: "tabacat" is not a palindrome.

In [19]:

class Solution:
    def isPalindrome(self, s: str) -> bool:
        l, r = 0, len(s) - 1
        s = s.lower()
        while l < r:
            # Skip non-alphanumeric characters on the left
            while l < r and not s[l].isalnum():
                l += 1
            # Skip non-alphanumeric characters on the right
            while l < r and not s[r].isalnum():
                r -= 1
            # Compare characters
            if s[l] != s[r]:
                return False
            # Move pointers
            l += 1
            r -= 1
        return True

In [20]:

print(isPalindrome("Was it a car or a cat I saw?"))

True

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