125. Valid Palindrome

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Problem

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.

Note: For the purpose of this problem, we define empty string as valid palindrome.

Example 1:

Input: "A man, a plan, a canal: Panama"
Output: true

Example 2:

Input: "race a car"
Output: false

Code

class Solution {
    public boolean isPalindrome(String s) {
        if(s == null || s.length() == 0) return true;

        int left = 0;
        int right = s.length() - 1;

        while(left < right){
            while(left < right && !Character.isLetterOrDigit(s.charAt(left))) left++;
            while(left < right && !Character.isLetterOrDigit(s.charAt(right))) right--;

            if(Character.toLowerCase(s.charAt(left))!= Character.toLowerCase(s.charAt(right))) return false;
            left++;
            right--;
        }

        return true;
    }
}