leetcode

0 class Solution {

1 public:

2 int fourSumCount(const vector<int> &nums1, const vector<int> &nums2, const vector<int> &nums3,

3 const vector<int> &nums4) const {

4 const int n = size(nums1);

5 unordered_map<int, int> um;

6 int res = 0;

7

8 for (int i = 0; i < n; i++) {

9 for (int j = 0; j < n; j++) {

10 um[nums1[i] + nums2[j]]++;

11 }

12 }

13

14 for (int i = 0; i < n; i++) {

15 for (int j = 0; j < n; j++) {

16 res += um[-(nums3[i] + nums4[j])];

17 }

18 }

19

20 return res;

21 }

22 };