滑动窗口

class Solution {
public:
    int longestSubstringWithoutDuplication(string s) {
        unordered_map<char, int> window;
        int left = 0, right = 0, res = 0;
        while(right < s.size()) {
            char c = s[right++];
            window[c]++;
            while(window[c] > 1) {
                char d = s[left++];
                window[d]--;
            }
            res = max(res, right-left);
        }
        return res;
    }
};