uva10105 多项式定理

#include <iostream>
#include <cstdio>
using namespace std;
typedef long long LL;
LL c[13][13];
void init(){
    for(int i = 0; i < 13; i++){
        c[i][0] = 1;
        for(int j = 1; j < i; j++)
            c[i][j] = c[i-1][j]+c[i-1][j-1];
        c[i][i] = 1;
    }
}
/**
C[][]
n!/(n1!*n2!*...*nk!)
**/
int main()
{
//    freopen("data.in", "r", stdin);
    int n, k, x;
    LL ans;
    init();
    while(scanf("%d%d", &n, &k) != EOF){
        ans = 1;
        while(k--){
            scanf("%d", &x);
            ans *= c[n][x];
            n-=x;
        }
        printf("%lld\n", ans);
    }
    return 0;
}