ValidPalindrome.java

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

Note: For the purpose of this problem, we define empty string as valid palindrome.

Example 1:

Input: "A man, a plan, a canal: Panama"
Output: true

USE TWO POINTERS!!

//TC: O(N)
//SC: O(1)

public class Solution {
    public boolean isPalindrome(String s) {
        if (s.isEmpty()) {
        	return true;
        }
        int head = 0, tail = s.length() - 1;
        char cHead, cTail;
        while(head <= tail) {
        	cHead = s.charAt(head);
        	cTail = s.charAt(tail);
        	if (!Character.isLetterOrDigit(cHead)) {
        		head++;
        	} else if(!Character.isLetterOrDigit(cTail)) {
        		tail--;
        	} else {
        		if (Character.toLowerCase(cHead) != Character.toLowerCase(cTail)) {
        			return false;
        		}
        		head++;
        		tail--;
        	}
        }
        return true;
    }
}