- Time limit: 1.00 s
- Memory limit: 512 MB
There are n cities and m flight connections between them. A city is called a critical city if it appears on every route from a city to another city.
Your task is to find all critical cities from Syrjälä to Lehmälä.
The first input line has two integers n and m: the number of cities and flights. The cities are numbered 1,2,\dots,n. City 1 is Syrjälä, and city n is Lehmälä.
Then, there are m lines describing the connections. Each line has two integers a and b: there is a flight from city a to city b. All flights are one-way.
You may assume that there is a route from Syrjälä to Lehmälä.
First print an integer k: the number of critical cities. After this, print k integers: the critical cities in increasing order.
- 2 \le n \le 10^5
- 1 \le m \le 2 \cdot 10^5
- 1 \le a,b \le n
5 5 1 2 2 3 2 4 3 5 4 5
3 1 2 5