- Time limit: 1.00 s
- Memory limit: 512 MB
There are n cities and m flight connections. Your task is to check if you can travel from any city to any other city using the available flights.
The first input line has two integers n and m: the number of cities and flights. The cities are numbered 1,2,\dots,n.
After this, there are m lines describing the flights. Each line has two integers a and b: there is a flight from city a to city b. All flights are one-way flights.
Print "YES" if all routes are possible, and "NO" otherwise. In the latter case also print two cities a and b such that you cannot travel from city a to city b. If there are several possible solutions, you can print any of them.
- 1 \le n \le 10^5
- 1 \le m \le 2 \cdot 10^5
- 1 \le a,b \le n
4 5 1 2 2 3 3 1 1 4 3 4
NO 4 2