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// 920. Number of Music Playlists
#include "leetcode.h"
/*
* 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, k', return the number of possible playlists that you can
* create. since the answer can be very large, return it modulo 10^9+7
*/
class Solution {
const int mod = 1e9 + 7;
long long solve(int n, int goal, int k, vvd & dp) {
if (!n && !goal)
return 1;
if (!n || !goal)
return 0;
if (dp[n][goal] != -1)
return dp[n][goal];
long long pick = solve(n - 1, goal - 1, k, dp) * n;
long long skip = solve(n, goal - 1, k, dp) * max(n - k, 0);
return dp[n][goal] = (pick + skip) % mod;
}
public:
int numMusicPlaylists(int n, int goal, int k) {
vvd dp(n + 1, vector<int>(goal + 1, -1));
return solve(n, goal, k, dp);
}
};
int main() {
Solution obj;
printf("%d\n", obj.numMusicPlaylists(3, 3, 1)); // expect: 6
printf("%d\n", obj.numMusicPlaylists(2, 3, 0)); // expect: 6
printf("%d\n", obj.numMusicPlaylists(2, 3, 1)); // expect: 2
}
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