LeetCode in Kotlin

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

class Solution {
    fun fourSumCount(nums1: IntArray, nums2: IntArray, nums3: IntArray, nums4: IntArray): Int {
        var count = 0
        val map: MutableMap<Int, Int> = HashMap()
        for (k in nums3) {
            for (i in nums4) {
                val sum = k + i
                map[sum] = map.getOrDefault(sum, 0) + 1
            }
        }
        for (k in nums1) {
            for (i in nums2) {
                val m = -(k + i)
                count += map.getOrDefault(m, 0)
            }
        }
        return count
    }
}

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