Create number-of-music-playlists.cpp

Author: kamyu104

C++/number-of-music-playlists.cpp

@@ -0,0 +1,22 @@
+// Time:  O(n * l)
+// Space: O(l)
+
+// Another better solution (generating function), you could refer to 
+// https://leetcode.com/problems/number-of-music-playlists/solution/
+
+class Solution {
+public:
+    int numMusicPlaylists(int N, int L, int K) {
+        static const int M = 1000000007;
+        vector<vector<uint64_t>> dp(2, vector<uint64_t>(1 + L, 0ull));
+        dp[0][0] = dp[1][1] = 1;
+        for (int n = 1; n <= N; ++n) {
+            dp[n % 2][n] = (dp[(n - 1) % 2][n - 1] * n) % M;
+            for (int l = n + 1; l <= L; ++l) {
+                dp[n % 2][l] = ((dp[n % 2][l - 1] * max(n - K, 0)) % M +
+                            (dp[(n - 1) % 2][l - 1] * n) % M) % M;
+            }
+        }
+        return dp[N % 2][L];
+    }
+};