# 0920. Number of Music Playlists

https://leetcode.com/problems/number-of-music-playlists

## Description

Your music player contains `n` different songs. You want to listen to `goal` songs (not necessarily different) during your trip. To avoid boredom, you will create a playlist so that:

* Every song is played **at least once**.
* A song can only be played again only if `k` other songs have been played.

Given `n`, `goal`, and `k`, return _the number of possible playlists that you can create_. Since the answer can be very large, return it **modulo** `109 + 7`.

**Example 1:**

```
**Input:** n = 3, goal = 3, k = 1
**Output:** 6
**Explanation:** There are 6 possible playlists: [1, 2, 3], [1, 3, 2], [2, 1, 3], [2, 3, 1], [3, 1, 2], and [3, 2, 1].
```

**Example 2:**

```
**Input:** n = 2, goal = 3, k = 0
**Output:** 6
**Explanation:** There are 6 possible playlists: [1, 1, 2], [1, 2, 1], [2, 1, 1], [2, 2, 1], [2, 1, 2], and [1, 2, 2].
```

**Example 3:**

```
**Input:** n = 2, goal = 3, k = 1
**Output:** 2
**Explanation:** There are 2 possible playlists: [1, 2, 1] and [2, 1, 2].
```

**Constraints:**

* `0 <= k < n <= goal <= 100`

## ac

```java
```
