'commit'

TangDou/AcWing_TiGao/T5/RongChi/214_1.cpp

@@ -0,0 +1,50 @@
+#include <bits/stdc++.h>
+using namespace std;
+#define int long long
+#define endl "\n"
+const int N = 20, mod = 1e9 + 7;
+
+int A[N];
+int n, m;
+
+// 快速幂
+int qmi(int a, int k) {
+    int res = 1;
+    while (k) {
+        if (k & 1) res = res * a % mod;
+        a = a * a % mod;
+        k >>= 1;
+    }
+    return res;
+}
+
+int C(int a, int b) {
+    if (a < b) return 0;
+    int up = 1, down = 1;
+    for (int i = a; i > a - b; i--) up = i % mod * up % mod;
+    for (int i = 1; i <= n - 1; i++) down = i * down % mod; //(n-1)! % mod
+    down = qmi(down, mod - 2);                              // 费马小定理求逆元
+
+    return up * down % mod; // 费马小定理
+}
+
+signed main() {
+    cin >> n >> m;
+    for (int i = 0; i < n; i++) cin >> A[i];
+
+    int res = C(n + m - 1, n - 1);
+    for (int i = 1; i < (1 << n); i++) {
+        int sum = 0, cnt = 0;
+        for (int j = 0; j < n; j++) {
+            if (i >> j & 1) {
+                sum += A[j] + 1;
+                cnt++;
+            }
+        }
+        if (cnt & 1)
+            res = (res - C(m + n - 1 - sum, n - 1) + mod) % mod;
+        else
+            res = (res + C(m + n - 1 - sum, n - 1)) % mod;
+    }
+    cout << res << endl;
+}