poj1306

简单题

#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;
}