Number of Sets of K Non-Overlapping Line Segments LeetCode solution in JavaScript

1
var numberOfSets = function (n, k) {
2
  return combinations(n + k - 1, 2 * k) % (1e9 + 7);
3
};
4
var combinations = (n, k) => {
5
  var dp = [...Array(n + 1)].map((d) => [...Array(k + 1)].map((d) => 1));
6
  for (let i = 1; i <= n; i++)
7
    for (let k = 1; k < i; k++)
8
      dp[i][k] = (dp[i - 1][k - 1] + dp[i - 1][k]) % (1e9 + 7);
9
  return dp[n][k];
10
};