Package g0601_0700.s0629_k_inverse_pairs_array

Class Solution

java.lang.Object
g0601_0700.s0629_k_inverse_pairs_array.Solution
public class Solution extends java.lang.Object
629 - K Inverse Pairs Array.

Hard

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

  • Constructor Summary

    Constructors
    Constructor
    Description
    Solution()
     

  • Method Summary

    Modifier and Type
    Method
    Description
    int
    kInversePairs(int n, int k)
     

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Constructor Details

    • Solution

      public Solution()

  • Method Details

    • kInversePairs

      public int kInversePairs(int n, int k)