#include <iostream>
#include <algorithm>
using namespace std;
 
int a[200001], b[200001], cnt[200001];
 
int main()
{
	int t;
	cin >> t;
	while (t--)
	{
		for (int i = 0; i < 200000; ++i)
		{
			cnt[i] = 0;
		}
		int n;
		cin >> n;
		for (int i = 0; i < n; ++i)
		{
			cin >> a[i];
		}
		for (int i = 0; i < n; ++i)
		{
			cin >> b[i];
		}
		sort(a, a + n);
		sort(b, b + n);
		int num = 0;
		for (int i = 0; i < n; ++i)
		{
			for (int j = num; j < n; ++j)
			{
				if (a[i] > b[j])
				{
					cnt[i] += 1;
					num += 1;
				}
			}
			cnt[i] += cnt[i - 1];
		}
		int ans = 1;
		for (int i = 0; i < n; ++i)
		{
			ans *= cnt[i] - i;
		}
		cout << ans << endl;
	}
	
	return 0;
}

我方法用的是乘法原理，为什么会错？