K Inverse Pairs Array LeetCode solution in Java

1
class Solution {
2
  public int kInversePairs(int n, int k) {
3
    int MOD = 1000000007;
4
    int[][] opt = new int[k + 1][n];
5
    for (int i = 0; i <= k; i++) {
6
      for (int j = 0; j < n; j++) {
7
        if (i == 0) {
8
          opt[i][j] = 1;
9
        } else if (j > 0) {
10
          opt[i][j] = (opt[i - 1][j] + opt[i][j - 1]) % MOD;
11
          if (i >= j + 1) {
12
            opt[i][j] = (opt[i][j] - opt[i - j - 1][j - 1] + MOD) % MOD;
13
          }
14
        }
15
      }
16
    }
17

18
    return opt[k][n - 1];
19
  }
20
}