125-Valid Palindrome

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.
水题一道..

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