629. K Inverse Pairs Array
Hard
1.9K
218

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 consist 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 <= 1000
  • 0 <= k <= 1000
Accepted
58.1K
Submissions
136.3K
Acceptance Rate
42.7%

Seen this question in a real interview before?
1/4
Yes
No

Discussion (0)

Related Topics
Copyright ©️ 2023 LeetCode All rights reserved