Valid Palindrome

Leetcode Problem 125: Valid Palindrome

Problem Summary

Given a string s, determine whether it is a valid palindrome after the following normalization:

1. Convert all uppercase letters to lowercase.
2. Remove all non-alphanumeric characters (keep only letters a–z and digits 0–9).
3. Check if the resulting string reads the same forwards and backwards.

Return true if the cleaned string is a palindrome, or false otherwise. An empty string (after cleaning) is considered a valid palindrome.

• The string length is between 1 and 200,000 characters.
• The string consists only of printable ASCII characters (any visible character or space).

Techniques

• Two Pointers
• String

Solution

function isPalindrome(s: string): boolean {
    let stringWithoutSpaces = s.replace(/[.,\/#!$%\^&\*;:{}=\-_`~()\s@;\"\[\]'\?]/g,"").toLowerCase()

    for (let i = 0, k = stringWithoutSpaces.length - 1; i < stringWithoutSpaces.length / 2; i++, k--) {
        if (stringWithoutSpaces.charAt(i) !== stringWithoutSpaces.charAt(k)) {
            return false
        }
    }

    return true
}

console.log(isPalindrome("A man, a plan, a canal: Panama"))
console.log(isPalindrome("race a car"))
console.log(isPalindrome(" "))