4710. [Jsoi2011] 分特产

https://hydro.ac/d/bzoj/record/63e0d2d9dd8145683f793e11

BZOJ/4710/4710.cpp

@@ -0,0 +1,53 @@
+#include <iostream>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 2005;
+const int mod = 1e9 + 7;
+
+int n, m, a[N], c[N][N], f[N], ans;
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    c[0][0] = 1;
+
+    for (int i = 1; i < N; ++i) {
+        c[i][0] = 1;
+
+        for (int j = 1; j <= i; ++j) {
+            c[i][j] = (static_cast<long long>(c[i - 1][j - 1]) + c[i - 1][j]) % mod;
+        }
+    }
+
+    cin >> n >> m;
+
+    for (int i = 1; i <= m; i++) {
+        cin >> a[i];
+    }
+
+    for (int i = 0; i < n; i++) {
+        f[i] = 1;
+
+        for (int j = 1; j <= m; j++) {
+            f[i] = static_cast<long long>(f[i]) * c[n - i + a[j] - 1][n - i - 1] % mod;
+        }
+
+        f[i] = static_cast<long long>(f[i]) * c[n][i] % mod;
+    }
+
+    for (int i = 0; i < n; i++) {
+        if (i % 2 == 0) {
+            ans = (static_cast<long long>(ans) + f[i]) % mod;
+        } else {
+            ans = (static_cast<long long>(ans) - f[i] + mod) % mod;
+        }
+    }
+
+    cout << ans << endl;
+
+    return 0;
+}