#include <bits/stdc++.h> using namespace std; const int MOD = 1000 * 1000 * 1000 + 7; void add(int &x, int v) { x += v; if (x >= MOD) { x -= MOD; } } void addProd(int &x, int a, int b) { x = (x + (long long) a * b) % MOD; } int solve(int n, int m) { vector <vector<int>> dp(2, vector <int> (n + 1, 0)); dp[1][0] = 1; for (int t = 0; t < n; t++) { vector <vector<int>> dpNew(2, vector <int> (n + 1, 0)); for (int full = 0; full <= 1; full++) { for (int numOpen = 0; numOpen <= min(t, m); numOpen++) { addProd(dpNew[1][numOpen], numOpen, dp[full][numOpen]); if (numOpen < m) { addProd(dpNew[0][numOpen + full], m - numOpen, dp[full][numOpen]); } } } dp = dpNew; } int ans = 0; for (int numOpen = 0; numOpen <= n; numOpen++) { add(ans, dp[1][numOpen]); } return ans; } int main() { ios_base::sync_with_stdio(false); int n, m; cin >> n >> m; cout << solve(n, m); return 0; }
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 | #include <bits/stdc++.h> using namespace std; const int MOD = 1000 * 1000 * 1000 + 7; void add(int &x, int v) { x += v; if (x >= MOD) { x -= MOD; } } void addProd(int &x, int a, int b) { x = (x + (long long) a * b) % MOD; } int solve(int n, int m) { vector <vector<int>> dp(2, vector <int> (n + 1, 0)); dp[1][0] = 1; for (int t = 0; t < n; t++) { vector <vector<int>> dpNew(2, vector <int> (n + 1, 0)); for (int full = 0; full <= 1; full++) { for (int numOpen = 0; numOpen <= min(t, m); numOpen++) { addProd(dpNew[1][numOpen], numOpen, dp[full][numOpen]); if (numOpen < m) { addProd(dpNew[0][numOpen + full], m - numOpen, dp[full][numOpen]); } } } dp = dpNew; } int ans = 0; for (int numOpen = 0; numOpen <= n; numOpen++) { add(ans, dp[1][numOpen]); } return ans; } int main() { ios_base::sync_with_stdio(false); int n, m; cin >> n >> m; cout << solve(n, m); return 0; } |