P4609 [FJOI2016]建筑师

https://www.luogu.com.cn/record/96923331

Luogu/P4609/P4609.cpp

@@ -0,0 +1,52 @@
+#include <iostream>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 5e4 + 5,
+          M = 205;
+const int mod = 1e9 + 7;
+
+int s[N][M], c[M][M];
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    s[0][0] = s[1][1] = 1;
+
+    for (int i = 2; i < N; i++) {
+        s[i][1] = static_cast<long long>(s[i - 1][1]) * (i - 1) % mod;
+    }
+
+    for (int i = 2; i < N; i++) {
+        for (int j = 1; j < M && j <= i; j++) {
+            s[i][j] = (static_cast<long long>(s[i - 1][j - 1]) + static_cast<long long>(s[i - 1][j]) * (i - 1)) % mod;
+        }
+    }
+
+    for (int i = 0; i < M; i++) {
+        c[i][0] = c[i][i] = 1;
+    }
+
+    for (int i = 2; i < M; i++) {
+        for (int j = 1; j < i; j++) {
+            c[i][j] = (static_cast<long long>(c[i - 1][j]) + c[i - 1][j - 1]) % mod;
+        }
+    }
+
+    int t;
+
+    cin >> t;
+
+    while (t--) {
+        int n, a, b;
+
+        cin >> n >> a >> b;
+
+        cout << static_cast<long long>(s[n - 1][a + b - 2]) * c[a + b - 2][a - 1] % mod << endl;
+    }
+
+    return 0;
+}