题解 | 抽卡

#include<bits/stdc++.h>
using namespace std;
using ll=long long;
const ll mod=1e9+7;

ll fast_pow(ll a,ll b,ll m){
    ll res=1;
    a%=m;

    while(b!=0){
        if(b&1){
            res=(res*a)%m;
        }
        a=(a*a)%m;
        b>>=1;
    }
    return res;
}

int main(){
    ios::sync_with_stdio(0),cin.tie(0),cout.tie(0);
    ll n;
    cin>>n;
    ll z=1,m=1;
    vector<ll>a(n+1);
    for(ll i=1;i<=n;i++){
        cin>>a[i];
        m=(m*a[i])%mod;
    }
    for(ll i=1;i<=n;i++){
        ll b;
        cin>>b;
        z=(z*(a[i]-b))%mod;
    }
    cout<<(1-z*fast_pow(m,mod-2,mod)%mod+mod)%mod;

    return 0;
}