class Solution(object):
 def lengthOfLongestSubstring(self, s):
 globalMax = -float('inf')
 globalSet = set()
 j = 0
 
 for i in range(len(s)):
 while j < len(s) and s[j] not in globalSet:
 globalSet.add(s[j])
 globalMax = max(globalMax, len(globalSet))
 j += 1
 globalSet.remove(s[i])
 
 return globalMax if globalMax != -float('inf') else 0