【2020模拟day8】A. 配对乘积

还蛮容易想到的

代码

#include<bits/stdc++.h>
using namespace std;
const int mod=1e9+7;
const int maxn=55;
long long n,a[maxn],b[maxn];
long long ans;
bool cmp(long long aa,long long bb)
{
	return aa>bb;
}
int main()
{
	freopen("c.in","r",stdin);
	freopen("c.out","w",stdout);
	int t; scanf("%d",&t);
	while(t--)
	{
		scanf("%lld",&n); ans=0;
		for(int i=1;i<=n;i++) scanf("%lld",&a[i]);
		for(int i=1;i<=n;i++) scanf("%lld",&b[i]);
		sort(a+2,a+n+1,cmp); sort(b+1,b+n+1);
		for(int i=1;i<=n;i++)
		{
			long long mul=a[1]*b[i];
			unsigned long long res=1;
			for(int j=2;j<=n;j++)
			{
				int pos=lower_bound(b+1,b+n+1,(double)mul/a[j])-b; 
				if(pos==n+1) pos--;
				if(b[pos]*a[j]>=mul) pos--;
				if(pos>=i) pos--;
				res=(1LL*res*(pos-j+2))%mod;
				if(!res) break;
			}
			ans=(ans+res)%mod;
		}
		printf("%lld\n",ans);
	}	
	
	return 0;
}