FourSumII454.kt

package 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
 */
fun fourSumCount(nums1: IntArray, nums2: IntArray, nums3: IntArray, nums4: IntArray): Int {
val map = HashMap<Int,Int>()

    nums1.forEach { num1->
        nums2.forEach { num2->
            val sum = num1+num2
            map[-sum]= (map[-sum]?:0)+1
        }
    }

    var count=0
    nums3.forEach { num3->
        nums4.forEach { num4->
            val sum=num3+num4
            count+=map[sum]?:0
        }
    }
    return count
}