76

class Solution {
public:
    string minWindow(string s, string t) {
        unordered_map<char, int> count;
        for(char c: t) count[c]++;
        int counter=t.size(), left, right;

        int ans=INT_MAX, idx=0;
        for(left=0, right=0; right<s.size(); right++){
            if(count[s[right]]-- > 0) counter--;
            while(counter == 0){
                if(right-left+1 < ans){
                    ans = min(ans, right-left+1);
                    idx = left;
                }
                if(count[s[left++]]++ == 0) counter++;
            }
        }
        return ans==INT_MAX ? "" : s.substr(idx,ans);
    }
};