125. Valid Palindrome

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

class Solution {
    public boolean isPalindrome(String s) {
        s = s.toLowerCase();
        int left = 0;
        int right = s.length() - 1;
        while (left < right) {
            if (!Character.isLetterOrDigit(s.charAt(left))) ++left;
            else if (!Character.isLetterOrDigit(s.charAt(right))) --right;
            else if (s.charAt(left) != s.charAt(right)) return false;
            else { ++left; --right; }
        }
        return true;
    }
}

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