003_Longest_Substring_Without_Repeating_Characters.py

class Solution:
    def lengthOfLongestSubstring(self, s: str) -> int:
        mapper = {}
        start = 0
        longest = 0
        
        for i, c in enumerate(s):
            if c in mapper and mapper[c] >= start:
                start = mapper[c] + 1
            else:
                longest = max(longest, i - start + 1)
            
            mapper[c] = i
        return longest