package problems.medium;
import java.util.HashMap;
import java.util.Map;
/**
* Created by sherxon on 1/13/17.
* Time complexity: O(n^2)
* Space complexity: O(n^2)
*/
public class FourSumII {
public int fourSumCount(int[] a, int[] b, int[] c, int[] d) {
Map<Integer, Integer> map = new HashMap<>();
for (int i = 0; i < a.length; i++)
for (int j = 0; j < b.length; j++)
if (!map.containsKey(a[i] + b[j]))
map.put(a[i] + b[j], 1);
else
map.put(a[i] + b[j], map.get(a[i] + b[j]) + 1);
int counter = 0;
for (int i = 0; i < c.length; i++)
for (int j = 0; j < d.length; j++) {
int target = 0 - (c[i] + d[j]);
if (map.containsKey(target))
counter += map.get(target);
}
return counter;
}
}