Submission #3388496

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Source Code Expand

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

int main() {
	const int MOD = 1000000007;
	int n;
	cin >> n;
	vector<ll> factorial(n+1, 1);
	for (int i = 2; i < n+1; ++i)
	{
		factorial[i] *= i;
		factorial[i] %= MOD;
	}

	vector<pair<ll, int> > ab(2 * n);
	for (int i = 0; i < n; ++i)
	{
		cin >> ab[i].first;
		ab[i].second = 1;
	}
	for (int i = n; i < 2 * n; ++i)
	{
		cin >> ab[i].first;
		ab[i].second = -1;
	}

	sort(ab.begin(), ab.end());

	int cnt = 0;
	int num = 0;
	ll ans = 1;

	for (int i = 0; i < 2*n; ++i)
	{
		cnt += ab[i].second;

		if (ab[i].second == 1 && cnt > 0)
		{
			num++;
		} else if (ab[i].second == -1 && cnt < 0)
		{
			num++;
		} else if (cnt == 0)
		{
			ans *= factorial[num];
			ans %= MOD;
			num = 0;
		}
	}

	cout << ans << endl;

	return 0;
}

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