LeetCode 125. Valid Palindrome

Question

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

For example, "A man, a plan, a canal: Panama" is a palindrome. "race a car" is not a palindrome.

Note: Have you consider that the string might be empty? This is a good question to ask during an interview.

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

Explanation

双指针问题。

Code

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