isPalindrome.js

/*

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.

 

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: s is an empty string "" after removing non-alphanumeric characters.
Since an empty string reads the same forward and backward, it is a palindrome.

*/

function isPalindrome(s) {
  const normalizedString = s.toLowerCase().replace(/[^a-zA-Z0-9]/g, '');
  if (normalizedString.length <= 1) return true;
  let end = normalizedString.length - 1;

  for (let i = 0; i < normalizedString.length; i++) {
    if (i === end) return true;

    if (normalizedString[i] !== normalizedString[end]) return false;

    end--;
  }
  return true;
}