Valid Palindrome

1public class Solution {
2    public bool IsPalindrome(string s) {
3        int i = 0;
4        int j = s.Length - 1;
5
6        while (i < j)
7        {
8            if (!Char.IsLetterOrDigit(s[i]))
9            {
10                i++;
11            }
12            if (!Char.IsLetterOrDigit(s[j]))
13            {
14                j--;
15            }
16            if (Char.IsLetterOrDigit(s[i]) && Char.IsLetterOrDigit(s[j]))
17            {
18                if (Char.ToLower(s[i]) != Char.ToLower(s[j]))
19                {
20                    return false;
21                }
22                else
23                {
24                    i++;
25                    j--;
26                }
27            }
28        }
29
30        return true;
31    }
32}

1class Solution {
2    // time O(n)
3    // space O(1)
4    public boolean isPalindrome(String s) {
5        int i = 0;
6        int j = s.length() - 1;
7
8        while (i < j) {
9            // The String.toLowerCase() method in Java has a time complexity of O(n), where n is the length of the string. Given n is always 1, O(1) here.
10            char ci = Character.toLowerCase(s.charAt(i));
11            char cj = Character.toLowerCase(s.charAt(j));
12
13            if (!Character.isLetterOrDigit(ci)) {
14                i++;
15            }
16            else if (!Character.isLetterOrDigit(cj)) {
17                j--;
18            }
19            else if (ci != cj) {
20                return false;
21            }
22            else {
23                i++;
24                j--;
25            }
26        }
27        return true;
28    }
29}