125-valid-palindrome-neetcode

125. Valid Palindrome (Easy) (https://leetcode.com/problems/valid-palindrome/)

A phrase is a palindrome if, after converting all uppercase letters into lowercase letters and removing all non-alphanumeric characters, it reads the same forward and backward. Alphanumeric characters include letters and numbers. Given a string s, return true if it is a palindrome, or false otherwise. Constraints: - 1 <= s.length <= 2 * 10^5 - s consists only of printable ASCII characters.

function isPalindrome(s: string): boolean {
  const cleaned = s.toLowerCase().replace(/[^a-z0-9]/g, '');
  let left = 0, right = cleaned.length - 1;
 
  while (left < right) {
    if (cleaned[left] !== cleaned[right]) return false;
    left++;
    right--;
  }
 
  return true;
}
 
// Local check:
console.log(isPalindrome("Was it a car or a cat I saw?")) // true
console.log(isPalindrome("tab a cat")) // false
console.log(isPalindrome(" ")) // true
console.log(isPalindrome("No lemon, no melon")) // true

Example 1:
 
    Input: s = "A man, a plan, a canal: Panama"
    Output: true
    Explanation: "amanaplanacanalpanama" is a palindrome.
 
  Example 2:
 
    Input: s = "race a car"
    Output: false
    Explanation: "raceacar" is not a palindrome.
 
  Example 3:
 
    Input: s = " "
    Output: true
    Explanation: An empty string is a palindrome.

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