哈希

# include <bits/stdc++.h>
using namespace std;
int n;
const int N = 5e5 + 10;
long long a[N], b[N];
long long prea[N], preb[N];
long long suma[N], sumb[N];
long long ret;
const long long MOD = 1000000007;
int main() {
	scanf("%d", &n);
	for (int i = 1; i <= n; i++) {
		scanf("%lld", &a[i]);
		prea[i] = (prea[i - 1] + a[i]) % MOD;
	}
	for (int i = 1; i <= n; i++) {
		scanf("%lld", &b[i]);
		preb[i] = (preb[i - 1] + b[i]) % MOD;
	}
	for (int i = 1; i <= n; i++) {
		(ret += (((n + 1) * prea[i]) % MOD) * preb[i]) %= MOD;
		suma[i] = (suma[i - 1] + prea[i]) % MOD;
		sumb[i] = (sumb[i - 1] + preb[i]) % MOD;
	}
	long long tot = (suma[n] * sumb[n]) % MOD;
	ret = (ret - tot + MOD) % MOD;
	printf("%lld", ret);
	return 0;
}

#include"bits/stdc++.h"
using namespace std;
int n；
long long a[500010],b[500010];
long long prea[500010],preb[500010];
long long suma,sumb;
long long ans;
#define mod 1000000007
int main()
{
	scanf("%d",&n);
	for(int i=1;i<=n;++i)
	{
		scanf("%lld",&a[i]);
		prea[i]=(prea[i-1]+a[i])%mod;
	}
	for(int i=1;i<=n;++i)
	{
		scanf("%lld",&b[i]);
		preb[i]=(preb[i-1]+b[i])%mod;
	}
	for(int i=1;i<=n;i++)
	{
		(ans+=(((n+1)*prea[i])%mod)*preb[i])%=mod;
		suma=(suma+prea[i])%mod;
		sumb=(sumb+preb[i])%mod;
	}
	long long tot=(suma[n]*sumb[n])%mod;
	ans=(ans-tot+mod)%mod;
	printf("%lld",ans);
	return 0；
}
//by fairicle