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.

Solution:

public class Solution {
    public boolean isPalindrome(String s) {
        if (s.isEmpty()) return true;

        int p1 = 0, p2 = s.length()-1;
　　　　 while (p1<s.length() && !( (s.charAt(p1)>='A' && s.charAt(p1)<='Z')  || (s.charAt(p1)>='a' && s.charAt(p1)<='z') || (s.charAt(p1)>='0' && s.charAt(p1)<='9') ) ) p1++;
 7　　　　　while (p2>=0 && !( (s.charAt(p2)>='A' && s.charAt(p2)<='Z')  || (s.charAt(p2)>='a' && s.charAt(p2)<='z') || (s.charAt(p2)>='0' && s.charAt(p2)<='9') ) ) p2--;

        while (p1<p2){
            char c1 = s.charAt(p1);
            char c2 = s.charAt(p2);
            if (c1 == c2 || Math.abs((int) c1 - (int) c2) == Math.abs( (int) 'A' - (int) 'a' ) ){
                p1++;
                p2--;
       　　　　 while (p1<s.length() && !( (s.charAt(p1)>='A' && s.charAt(p1)<='Z')  || (s.charAt(p1)>='a' && s.charAt(p1)<='z') || (s.charAt(p1)>='0' && s.charAt(p1)<='9') ) ) p1++;
　　　　　　　　 while (p2>=0 && !( (s.charAt(p2)>='A' && s.charAt(p2)<='Z')  || (s.charAt(p2)>='a' && s.charAt(p2)<='z') || (s.charAt(p2)>='0' && s.charAt(p2)<='9') ) ) p2--;
　　　　　　　} else return false;
        }

        return true;
    }
}