public class Solution {
    public int LengthOfLongestSubstring(string s) {
        int max = 0;
        int n = 0;
        for (int i = 0; i < s.Length; i++)
        {
            n++;
            if (n > 1)
            {
                n -= FindDuplicateCharacter(s.Substring(i - n + 1, n)) + 1;
            }
            if (n > max) {
                max = n;
            }
        }
        return max;
    }

    public int FindDuplicateCharacter(string s) {
        char last = s[s.Length - 1];
        for (int i = 0; i < s.Length - 1; i++)
        {
            if (s[i] == last)
            {
                return i;
            }
        }
        return -1;
    }
}