class Solution {
public int fourSumCount(int[] A, int[] B, int[] C, int[] D) {
int n = A.length;
Map map = new HashMap<>();
for (int i = 0; i < n; i++) {
for (int j = 0; j < n; j++) {
map.put(A[i] + B[j], map.getOrDefault(A[i] + B[j], 0) + 1);
}
}
int count = 0;
for (int i = 0; i < n; i++) {
for (int j = 0; j < n; j++) {
count += map.getOrDefault(-1 * (C[i] + D[j]), 0);
}
}
return count;
}
}