class Solution { public int fourSumCount(int[] A, int[] B, int[] C, int[] D) { Map map = new HashMap<>(); int count = 0; for (int a : A) { for (int b : B) { if (!map.containsKey(a+b)) { map.put(a+b, 1); } else { map.put(a+b, map.get(a+b) + 1); } } } for (int c : C) { for (int d : D) { if (map.containsKey(0 - (c+d))) { count += map.get(0-(c+d)); } } } return count; }}
class Solution { public int fourSumCount(int[] A, int[] B, int[] C, int[] D) { Map map = new HashMap<>(); int count = 0; for (int a : A) { for (int b : B) { if (!map.containsKey(a+b)) { map.put(a+b, 1); } else { map.put(a+b, map.get(a+b) + 1); } } } for (int c : C) { for (int d : D) { if (map.containsKey(0 - (c+d))) { count += map.get(0-(c+d)); } } } return count; }}