package leetcode.array;

import java.util.HashMap;

import java.util.Map;

/**

* @ClassName FourSum

* @Description 四数相加 https://leetcode-cn.com/problems/4sum-ii/

* @Author changxuan

* @Date 2020/11/27 下午10:56

**/

public class FourSum {

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

Map<Integer, Integer> map = new HashMap<>();

//Map<Integer, Integer> map = new HashMap<>();

int res = 0;

for(int i = 0;i<A.length;i++){

for(int j= 0;j<B.length;j++){

int sumAB = A[i]+B[j];

if(map.containsKey(sumAB)) map.put(sumAB,map.get(sumAB)+1);

else map.put(sumAB,1);

}

}

for(int i = 0;i<C.length;i++){

for(int j = 0;j<D.length;j++){

int sumCD = -(C[i]+D[j]);

if(map.containsKey(sumCD)) res += map.get(sumCD);

}

}

return res;

}

}