leetcode/4sum.cc at master · luokn/leetcode · GitHub

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#include "leetcode.h"

using namespace std;

class Solution {
  public:
    int fourSumCount(vector<int> &A, vector<int> &B, vector<int> &C, vector<int> &D) {
        int           counter = 0;
        map<int, int> sum_map;
        for (const auto a : A) {
            for (const auto b : B) { ++sum_map[a + b]; }
        }
        for (const auto c : C) {
            for (const auto d : D) { counter += sum_map[-(c + d)]; }
        }
        return counter;
    }
};

int main(int argc, char const *argv[]) {
    Solution    solution;
    vector<int> a{0, 1, -1};
    vector<int> b{-1, 1, 0};
    vector<int> c{0, 0, 1};
    vector<int> d{-1, 1, 1};
    cout << solution.fourSumCount(a, b, c, d) << endl;
}