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

        #TC: O(n)
        #SC: max(O(n)) n = len(s)

        if len(s) == 0:
            return 0

        left = 0
        right = 1

        Dict = {}
        Dict[s[left]] = 1
        res = 1

        count = 0

        while(right < len(s)):
            if s[right] not in Dict:
                Dict[s[right]] = 1
                if count == 0:
                    Len = right - left + 1
                    res = max(res, Len)
            else:
                Dict[s[right]] += 1
                if Dict[s[right]] == 2:
                    count += 1

                while(left < right):
                    left += 1
                    Dict[s[left-1]] -= 1
                    if Dict[s[left-1]] == 0:
                        del Dict[s[left-1]]
                    elif Dict[s[left-1]] == 1:
                        count -= 1
                        if count == 0:
                            Len = right - left + 1
                            break
            right += 1

        return res