[Lintcode]Valid Parentheses

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.

public class Solution {
    /**
     * @param s A string
     * @return Whether the string is a valid palindrome
     */
    public boolean isPalindrome(String s) {
        int left = 0, right = s.length() - 1;
        char[] str = s.toCharArray();
        
        while(left < right) {
            while(left < right &&
            str[left] < 'A' || (str[left] > 'Z' && str[left] < 'a') || str[left] > 'z' ) {
                if(str[left] >= '0' && str[left] <= '9') break;//考虑数字问题
                left++;
            }
            
            while(right > left &&
            str[right] < 'A' || (str[right] > 'Z' && str[right] < 'a') || str[right] > 'z' ) {
                if(str[right] >= '0' && str[right] <= '9') break;
                right--;
            }
            
            if(left == right) return true;
            
            if(left < right) {
                //考虑大小写问题
                if(Math.abs(str[left] - str[right]) != 32 && Math.abs(str[left] - str[right]) != 0)
                    return false;
                    
                left++;
                right--;    
            }
            
            else return false;
        }
        return true;
    }
}