[C++] STL makes good


  • 0
    Y
    class FourSum {
    public:
        int fourSumCount(vector<int>& A, vector<int>& B, vector<int>& C, vector<int>& D) {
            
            unordered_map<int, int> ab, cd;
            for (int i : A) for (int j : B) ab[i+j]++;
            for (int i : C) for (int j : D) cd[i+j]++;
    
            int res = 0;
            for (auto i : ab)
                res += i.second * cd[-i.first];
            
            return res;
        }
    };
    

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