class Solution(object):
  def lengthOfLongestSubstring(self, s):
    max_sub_length = 0
    start = 0
    s_length = len(s)
    
    for end in range(1, s_length):
      if s[end] in s[start:end]:
        start = s[start:end].index(s[end]) + 1 + start
      else:
        max_sub_length = max(max_sub_length, end - start + 1)
	return max_sub_length