3. Longest Substring Without Repeating Characters

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class Solution:
    def lengthOfLongestSubstring(self, s: str) -> int:

        M = defaultdict(int)
        l = -1
        res = 0

        for i in range(len(s)):
            if s[i] in M:
                l = max(l, M[s[i]])

            res = max(res, i - l)
            M[s[i]] = i

        return res