Submission #1837463

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Source Code Expand

#include<bits/stdc++.h>
#define range(i,a,b) for(int i = (a); i < (b); i++)
#define rep(i,b) for(int i = 0; i < (b); i++)
#define all(a) (a).begin(), (a).end()
#define show(x)  cerr << #x << " = " << (x) << endl;
//const int INF = 1e8;
using namespace std;

const int M = 1000000007;

//x^n mod M
typedef long long ull;
ull power(ull x, ull n, ull M){
	ull res = 1;
	if(n > 0){
		res = power(x, n / 2, M);
		if(n % 2 == 0) res = (res * res) % M;
		else res = (((res * res) % M) * x ) %M;
	}
	return res;
}

int main(){
	int n;
	cin >> n;

	vector<int> a(n), b(n);
	vector<pair<int, bool>> p(n * 2); //1 : PC, 0 : power supply
	rep(i,n){
		cin >> a[i] >> b[i];
	}

	rep(i,n){
		p[i] = make_pair(a[i], true);
		p[i + n] = make_pair(b[i], false);
	}

	sort(all(p));

	int cnt = 0, cur = -1;
	vector<int> v;
	rep(i,n){
		cnt += p[i].second ? 1 : -1;
		if(cnt == 0){
			v.emplace_back((i - cur) / 2);
			cur = i;
		}
	}

	//for(auto i : p){ cout << i.second << ' ' ; } cout << endl;

	long long ans = 1;
	for(auto i : v){
		//show(i)
		vector<long long> c(i);
		rep(j,i + 1){
			if(j == 0) c[j] = 1;
			else{
				c[j] = c[j - 1] * (i - (j - 1)) % M * power(j, M - 2, M) % M;
			}
		}

		long long m = 1;
		rep(j,i){
			m *= c[j];
			m %= M;
		}
		(ans *= m) %= M;
	}
	cout << ans << endl;
}

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