LeetCode-in-Java

454. 4Sum II

Medium

Given four integer arrays nums1, nums2, nums3, and nums4 all of length n, return the number of tuples (i, j, k, l) such that:

• 0 <= i, j, k, l < n
• nums1[i] + nums2[j] + nums3[k] + nums4[l] == 0

Example 1:

Input: nums1 = [1,2], nums2 = [-2,-1], nums3 = [-1,2], nums4 = [0,2]

Output: 2

Explanation: The two tuples are:

1. (0, 0, 0, 1) -> nums1[0] + nums2[0] + nums3[0] + nums4[1] = 1 + (-2) + (-1) + 2 = 0

2. (1, 1, 0, 0) -> nums1[1] + nums2[1] + nums3[0] + nums4[0] = 2 + (-1) + (-1) + 0 = 0

Example 2:

Input: nums1 = [0], nums2 = [0], nums3 = [0], nums4 = [0]

Output: 1

Constraints:

• n == nums1.length
• n == nums2.length
• n == nums3.length
• n == nums4.length
• 1 <= n <= 200
• -228 <= nums1[i], nums2[i], nums3[i], nums4[i] <= 228

Solution

import java.util.HashMap;
import java.util.Map;

public class Solution {
    public int fourSumCount(int[] nums1, int[] nums2, int[] nums3, int[] nums4) {
        int count = 0;
        Map<Integer, Integer> map = new HashMap<>();
        for (int k : nums3) {
            for (int i : nums4) {
                int sum = k + i;
                map.put(sum, map.getOrDefault(sum, 0) + 1);
            }
        }
        for (int k : nums1) {
            for (int i : nums2) {
                int m = -(k + i);
                count += map.getOrDefault(m, 0);
            }
        }
        return count;
    }
}

This site is open source. Improve this page.