tsanmmmm2000's Tech Blog

Question

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.

My C# Solution

public class Solution {
    public bool IsPalindrome(string s) {

        if (String.IsNullOrEmpty(s)) return true;
        
        var sChars = s.ToCharArray();
        var head = 0;
        var tail = s.Length - 1; 
        while(head < tail)
        {
            var headChar = sChars[head];
            var tailChar = sChars[tail];
            if (!Char.IsLetterOrDigit(headChar))
            {
                head++;
                continue;
            }
            
            if (!Char.IsLetterOrDigit(tailChar))
            {
                tail--;
                continue;
            }
            
            if (Char.ToLower(headChar) != Char.ToLower(tailChar)) 
            {
                return false;                
            }
            
            head++;
            tail--;
        }
        return true;
    }
}