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Java-based LeetCode algorithm problem solutions, regularly updated

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package g0401_0500.s0454_4sum_ii;

// #Medium #Top_Interview_Questions #Array #Hash_Table
// #2022_07_18_Time_133_ms_(95.19%)_Space_42.4_MB_(88.53%)

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

/**
 * 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
**/
public class Solution {
    public int fourSumCount(int[] nums1, int[] nums2, int[] nums3, int[] nums4) {
        int count = 0;
        Map 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;
    }
}