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