Leetcode[Easy] - Valid Palindrome

public class Solution {
    public boolean isPalindrome(String s) {
        int n = s.length(); char x,y;
        for(int i=0,j=n-1; i<j; ){
            x = s.charAt(i);
            y = s.charAt(j);
            if(!('A'<=x && x<='Z'||'a'<=x && x<='z'||'0'<=x && x<='9'))
            {
                i++;
                continue;
            }
            if(!('A'<=y && y<='Z'||'a'<=y && y<='z'||'0'<=y && y<='9'))
            {
                j--;
                continue;
            }
            if(!(x+"").toLowerCase().equals((y+"").toLowerCase()))
                return false;
            else{
                i++;
                j--;
            } 
        }
        return true;
    }
}

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HINT:

貌似是考正则表达式的，失策！！！

toLowerCase(); 

equals()

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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.