Overview

Given a string s, return true if it is a palindrome after converting all uppercase letters to lowercase and removing all non-alphanumeric characters. Otherwise return false.

Constraints

• 1 <= s.length <= 200,000
• s consists of printable ASCII characters.
• Only alphanumeric characters are considered for the palindrome check.

Examples

isPalindrome("A man, a plan, a canal: Panama");
// => true  ("amanaplanacanalpanama")

isPalindrome("race a car");
// => false

isPalindrome(" ");
// => true  (empty after stripping → trivially a palindrome)

Solution

function isPalindrome(s) {
  const clean = s.toLowerCase().replace(/[^a-z0-9]/g, "");
  let l = 0, r = clean.length - 1;
  while (l < r) {
    if (clean[l] !== clean[r]) return false;
    l++;
    r--;
  }
  return true;
}

Resources

• Valid Palindrome — LeetCode
• Palindrome — Wikipedia