以下是我的代碼：
#include<stdio.h>
const long maxn=17;
long d[maxn][maxn];
void init()
{
for(long i=0;i<maxn;i++)
d[i][0]=d[i][i]=1;
for(long i=2;i<maxn;i++)
for(long j=1;j<i;j++)
d[i][j]=d[i-1][j]+d[i-1][j-1];
}
long C(long n,long k)
{
return d[n][k];
}
int main()
{
/*
freopen("data.in","r",stdin);
freopen("data.out","w",stdout);
//*/
long n,k,ans,a[maxn];
init();
while(scanf("%ld%ld",&n,&k)==2)
{
for(long i=1;i<=k;i++) scanf("%ld",&a[i]);
ans=1;
for(long i=1;i<=k;i++)
{
ans*=C(n,a[i]);
n-=a[i];
}
printf("%ld\n",ans);
}
return 0;
}