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4Sum II Tuple Count

SambaNova Systems● MediumNEW GRADONSITE INTERVIEW

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Problem statement

Given four integer arrays, count index tuples (i, j, k, l) such that nums1[i] + nums2[j] + nums3[k] + nums4[l] == 0.

Equal values at different indices represent different tuples. Return the count as a 64-bit integer.

Function

fourSumCount(nums1: int[], nums2: int[], nums3: int[], nums4: int[]) → long

Examples

Example 1

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

There are two complementary pair combinations.

Example 2

nums1 = [0]nums2 = [0]nums3 = [0]nums4 = [0]return = 1

The single tuple sums to zero.

Example 3

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

The equal ones occur at two distinct indices.

Constraints

1 <= nums1.length, nums2.length, nums3.length, nums4.length <= 500.
-10^9 <= numsX[i] <= 10^9.
The returned count fits in a signed 64-bit integer.