https://www.luogu.com.cn/record/220838041

#include <iostream>
using namespace std;
typedef long long ll;
const ll N=1010;
const ll mod=1e9+7;
ll T;
ll n,m;
ll a[N];
ll c[N][N]; 
ll ans;
int main()
{
    cin>>T;
    for(ll i=0;i<N;i++)
    {
        for(ll j=0;j<=i;j++)
        {
            if(j==0)
            {
                c[i][j]=1;
            }
            else
            {
                c[i][j]=c[i-1][j]+c[i-1][j-1];
            }
        }
    }
    while(T--)
    {
        cin>>n>>m;
        ll sum=0;
        ans=1;
        for(ll i=1;i<=m;i++)
        {
            cin>>a[i];sum+=a[i];
        }
        if(sum>n) n++;
        for(ll i=1;i<=m;i++)
        {
            ans=(ll)((c[n][a[i]]*ans)%mod);
            n-=a[i];
        }
        cout<<ans%mod<<'\n';
    }
    
    return 0;
}