_629.java

package com.fishercoder.solutions;

/**
 * 629. K Inverse Pairs Array
 *
 * Given two integers n and k, find how many different arrays consist of numbers from 1 to n such that there are exactly k inverse pairs.
 We define an inverse pair as following: For ith and jth element in the array,
 if i < j and a[i] > a[j] then it's an inverse pair; Otherwise, it's not.
 Since the answer may very large, the answer should be 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 pair.

 Example 2:
 Input: n = 3, k = 1
 Output: 2
 Explanation:
 The array [1,3,2] and [2,1,3] have exactly 1 inverse pair.

 Note:
 The integer n is in the range [1, 1000] and k is in the range [0, 1000].
 */
public class _629 {

    public int kInversePairs(int n, int k) {
        return 0;
    }
}