HDU 3037 Saving Beans（Lucas定理模板题）

 1 #include <cstdio>
 2 #include <algorithm>
 3 #include <cstring>
 4 #include <iostream>
 5 using namespace std;
 6 typedef long long LL;
 7 
 8 const int MAXN = 100010;
 9 
10 int fac[MAXN];
11 int n, m, p, T;
12 
13 int power(int x, int p, int mod) {
14     int res = 1;
15     while(p) {
16         if(p & 1) res = (LL)res * x % mod;
17         x = (LL)x * x % mod;
18         p >>= 1;
19     }
20     return res;
21 }
22 
23 void init_fac(int p) {
24     fac[0] = 1;
25     for(int i = 1; i <= p; ++i)
26         fac[i] = (LL)fac[i - 1] * i % p;
27 }
28 
29 int lucas(int n, int m, int p) {
30     int res = 1;
31     while(n && m) {
32         int a = n % p, b = m % p;
33         if(a < b) return 0;
34         res = (LL)res * fac[a] * power((LL)fac[b] * fac[a - b] % p, p - 2, p) % p;//三次乘法注意
35         n /= p;
36         m /= p;
37     }
38     return res;
39 }
40 
41 int main() {
42     scanf("%d", &T);
43     while(T--) {
44         scanf("%d%d%d", &n, &m, &p);
45         init_fac(p);
46         printf("%d\n", lucas(n + m, m, p));
47     }
48 }