lc454 class Solution { public int fourSumCount(int[] nums1, int[] nums2, int[] nums3, int[] nums4) { Map<Integer,Integer> abmap=new HashMap<>(); for (int i = 0; i < nums1.length; i++) { for (int j = 0; j < nums2.length; j++) { if (!abmap.containsKey(nums1[i]+nums2[j])){ abmap.put(n...