leetcode454

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;
    }
}

https://leetcode.com/problems/4sum-ii/#/description

补充一个python的版本：

 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