poj1306

简单题

View Code

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
using namespace std;

long long com(long long n, long long r)
{
if (n - r < r)
r = n - r;
long long i, j, s = 1;
for (i = 0, j = 1; i < r; ++i)
{
s *= (n - i);
for (; j <= r && s % j == 0; ++j)
s /= j;
}
return s;
}

int main()
{
//freopen("t.txt", "r", stdin);
long long m, n;
while (scanf("%lld%lld", &m, &n), m | n)
printf("%lld things taken %lld at a time is %lld exactly.\n", m, n, com(m, n));
return 0;
}