'commit'

TangDou/AcWing/Math/ZhuHeJiShu/Test.cpp

@@ -0,0 +1,33 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+const int INF = 0x3f3f3f3f;
+typedef long long LL;
+const int N = 1e5 + 10;
+const int mod = 1e9 + 7;
+int fact[N];
+int infact[N];
+int qmi(int a, int k, int p) {
+    int res = 1;
+    while (k) {
+        if (k & 1) res = (LL)res * a % p;
+        a = (LL)a * a % p;
+        k >>= 1;
+    }
+    return res;
+}
+int main() {
+    fact[0] = infact[0] = 1;
+    for (int i = 1; i < N; i++) {
+        fact[i] = (LL)fact[i - 1] * i % mod;
+        infact[i] = (LL)infact[i - 1] * qmi(i, mod - 2, mod) % mod;
+    }
+    int n;
+    scanf("%d", &n);
+    while (n--) {
+        int a, b;
+        scanf("%d %d", &a, &b);
+        printf("%d\n", (LL)fact[a] * infact[b] % mod * infact[a - b] % mod);
+    }
+    return 0;
+}