CODE

public class Solution {
  public int LengthOfLongestSubstring(string s) {

    int window_size = 1;
    int max_window_size = s.Length;

    if (s.Length == 0)
      return 0;

    int longest = 1;

    while (window_size < max_window_size)
    {
      int i = 0;
      int j = i + window_size;
      while (i + window_size < s.Length)
      {
        int length = checkDups(s, i, j);
        if (length > 0)
          longest = length;
        i++;
        j = i + window_size;
      }       
      window_size++;
    }
    return longest;
  }

  private int checkDups(string s, int start, int end)
  {
    char[] windowChars = new char[end-start + 1];
    int j = 0;
    for (int i = start; i < end + 1; i++)
      windowChars[j++] = s[i];
    
    Array.Sort(windowChars);
    for (int i = 0; i < windowChars.Length - 1; i++)
      if (windowChars[i] == windowChars[i+1])
      {
        return -1;
      }
    
    return (end-start + 1);
  }
}