1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
#include<bits/stdc++.h>
using namespace std;

int tab[1000009], col[500009];
vector<int> graf[500009];
queue<int> q;
const long long M = 1e9 + 7;

long long fast_pow(long long a, long long p)
{
	if(p == 0) return 1;
	if(p == 1) return a;
	long long b = fast_pow(a, p/2);
	if(p % 2 == 1) b = (((b * b) % M) * a) % M;
	else b = (b * b) % M;
	return b;
}

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0); cout.tie(0);
	int n, a, b, c, wyn = 0;
	cin>>n;
	for(int i=1; i<=n; i++)
	{
		cin>>a>>b;
		if(tab[a] > 0) graf[tab[a]].push_back(i);
		if(tab[b] > 0) graf[tab[b]].push_back(i);
		for(int j=a; j<=b; j++) tab[j] = i;
	}
	for(int i=1; i<=n; i++)
	{
		col[i] = i;
		q.push(i);
		a = 0;
		while(!q.empty())
		{
			b = q.front();
			q.pop();
			a++;
			for(int j=0; j<graf[b].size(); j++)
			{
				c = graf[b][j];
				if(col[c] < i)
				{
					col[c] = i;
					q.push(c);
				}
			}
		}
		wyn = (wyn + fast_pow(a, M-2)) % M;
	}
	cout<<wyn;
    return 0;
}