class Solution {
public:
    int longestSubstringWithoutDuplication(string s) {
        unordered_map<char, int> hash;
        int n = s.size(), res = 0;

        for (int i = 0, j = 0; i < n; i ++) {
            hash[s[i]]++;
            while (hash[s[i]] > 1) {
                hash[s[j]]--;
                j++;
            }
            res = max(res, i - j + 1);
        }
        return res;

    }
};