leetcode--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.

难点在于判断是不是字母和数字以及比较的时候大小字母全部弄到一样做处理。

public class Solution {
    public boolean isPalindrome(String s) {
      if(s.length()==0) return true;
      char[] c=s.toCharArray();
      int i=0;
      int j=c.length-1;
       while(i<j){
           if(!Character.isLetterOrDigit(c[i])){
               i++;
               continue;
           }
          if(!Character.isLetterOrDigit(c[j])){
              j--;
              continue;
          } 
          if(Character.toLowerCase(c[i])!=Character.toLowerCase(c[j])){
              return false; 
          }
           i++;
           j--;
       }
       return true;
    }
}