Watch 10 video solutions for K Inverse Pairs Array, a hard level problem involving Dynamic Programming. This walkthrough by NeetCodeIO has 17,603 views views. Want to try solving it yourself? Practice on FleetCode or read the detailed text solution.
For an integer array nums, an inverse pair is a pair of integers [i, j] where 0 <= i < j < nums.length and nums[i] > nums[j].
Given two integers n and k, return the number of different arrays consisting of numbers from 1 to n such that there are exactly k inverse pairs. Since the answer can be huge, return it modulo 109 + 7.
Example 1:
Input: n = 3, k = 0 Output: 1 Explanation: Only the array [1,2,3] which consists of numbers from 1 to 3 has exactly 0 inverse pairs.
Example 2:
Input: n = 3, k = 1 Output: 2 Explanation: The array [1,3,2] and [2,1,3] have exactly 1 inverse pair.
Constraints:
1 <= n <= 10000 <= k <= 1000