_125.java

package com.fishercoder.solutions;

/**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.*/
public class _125 {

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

}