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"isnota 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.

代码

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;
    }
}