Valid Palindrome

Problem Statement

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.

Run Time Complexity

Run time is O(n)

Code

public class Solution {
    public boolean isPalindrome(String s) {
        if(s.length() < 1){
            return true;
        }
        
        int start = 0;
        int end = s.length()-1;
        while(start < end){
            char char1 = Character.toLowerCase(s.charAt(start));
            char char2 = Character.toLowerCase(s.charAt(end));
            
            if(!Character.isLetter(char1) && !Character.isDigit(char1)){
                start++;
            }
            else if(!Character.isLetter(char2) && !Character.isDigit(char2)){
                end--;
            }
            else if(char1 == char2){
                start++;
                end--;
            }else{
                return false;
            }
            
        }return true;
        
    }
}