Your music player contains N different songs and she wants to listen to
L (not necessarily different) songs during your trip. You create a
playlist so that:
K other songs have been
played
Return the number of possible playlists. As the answer can be very large,
return it modulo 10^9 + 7.
Example 1:
Input: N = 3, L = 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], [3, 2, 1].
Example 2:
Input: N = 2, L = 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], [1, 2, 2]
Example 3:
Input: N = 2, L = 3, K = 1 Output: 2 Explanation: There are 2 possible playlists. [1, 2, 1], [2, 1, 2]