public class Solution {

    public int FourSumCount(int[] A, int[] B, int[] C, int[] D) {

        var dic = new Dictionary<int, int>();

            for (int i = ; i < C.Length; i++)

            {

                for (int j = ; j < D.Length; j++)

                {

                    int sum = C[i] + D[j];

                    if (!dic.ContainsKey(sum))

                    {

                        dic.Add(sum, );

                    }

                    else

                    {

                        dic[sum]++;

                    }

                }

            }

            int res = ;

            for (int i = ; i < A.Length; i++)

            {

                for (int j = ; j < B.Length; j++)

                {

                    var cur = ;

                    var oppo = - * (A[i] + B[j]);

                    if (dic.ContainsKey(oppo))

                    {

                        cur = dic[oppo];

                    }

                    res += cur;

                }

            }

            return res;

    }

}

 class Solution:

     def fourSumCount(self, A: 'List[int]', B: 'List[int]', C: 'List[int]', D: 'List[int]') -> int:

         partone = {}

         res =

         for a in A:

             for b in B:

                 cur = a + b

                 if cur in partone:

                     partone[cur] +=

                 else:

                     partone[cur] = 

         for c in C:

             for d in D:

                 cur = c + d

                 if -cur in partone:

                     res += partone[-cur]

         return res