hdu 3037 Saving Beans(组合数学)

hdu 3037 Saving Beans

题目大意:n个数,和不大于m的情况,结果模掉p,p保证为素数。

解题思路:隔板法,C(nn+m)多选的一块保证了n个数的和小于等于m。可是n,m非常大,所以用到Lucas定理

#include <cstdio>
#include <cstring>
#include <algorithm> using namespace std;
typedef long long ll; ll n, m, p; ll qPow (ll a, ll k) {
ll ans = 1; while (k) {
if (k&1)
ans = (ans * a) % p;
a = (a * a) % p;
k /= 2;
}
return ans;
} /*
long long qPow(long long a, long long k) {
if (k == 0) return 1;
if (k == 1) return a;
long long ans = qPow(a * a % p, k>>1);
if (k&1) ans = ans * a % p;
return ans;
}
*/ ll C (ll a, ll b) { if (a < b)
return 0; if (b > a - b)
b = a - b; ll up = 1, down = 1; for (ll i = 0; i < b; i++) {
up = up * (a-i) % p;
down = down * (i+1) % p;
}
return up * qPow(down, p-2) % p;
} ll lucas (ll a, ll b, ll p) {
if (b == 0)
return 1;
return C(a%p, b%p) * lucas(a/p, b/p, p) % p;
} int main () {
int cas;
scanf("%d", &cas);
while (cas--) {
scanf("%lld%lld%lld", &n, &m, &p);
printf("%lld\n", lucas(n+m, m, p));
}
return 0;
}
上一篇:maven引入spring相关依赖


下一篇:微信小程序开发学习(一)