SPOJ MARBLES(简单组合)

暑期个人赛第四场

题意：把n个求分给k个颜色，

思路：转化一下，将球的n-1个空隙插上隔板，那么答案就是c(n-1,k-1);

代码如下：

#include <cstdio>
long long c(int n, int k)
{
    if(n-k<k) k = n-k;
    double ans = 1;
    for(int i = 1; i <= k; i++) ans*=1.0*(n-i+1)/i;
    return (long long)(ans+0.5);
}
int main ()
{
    int n, k, t;
    scanf("%d", &t);
    while(t--)
    {
        scanf("%d %d",&n,&k);
        printf("%lld\n", c(n-1,k-1));
    }
    return 0;
}

代码如下：

#include <cstdio>
double c(int n, int k)
{
    if(n-k<k) k = n-k;
    double c = 1.0;
    for(int i = 1; i <= k; ++i) c = c*(n-i+1)/i;
    return c;
}
int main ()
{
    int n, k, t;
    scanf("%d", &t);
    while(t--)
    {
        scanf("%d %d",&n,&k);
        printf("%lld\n", c(n-1,k-1));
    }
    return 0;
}