Valid Palindrome

题目:

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.

 1 public class Solution {
 2     public boolean isPalindrome(String s) 
 3     {
 4         int i = 0;
 5         int j = s.length()-1;
 6         while(i<j)
 7         {
 8             while(i<j&&!Character.isLetterOrDigit(s.charAt(i))) i++;
 9             while(i<j&&!Character.isLetterOrDigit(s.charAt(j))) j--;
10             if(Character.toLowerCase(s.charAt(i))!=Character.toLowerCase(s.charAt(j)))return false;
11             i++;j--;
12         }
13 
14         return true;
15     }
16 }

reference: Clean Code Handbook