- Time limit: 1.00 s
- Memory limit: 512 MB
Your task is to find out the minimum number of roads required, and also determine which roads should be built.
The first input line has two integers $n$ and $m$: the number of cities and roads. The cities are numbered $1,2,\dots,n$.
After that, there are $m$ lines describing the roads. Each line has two integers $a$ and $b$: there is a road between those cities.
A road always connects two different cities, and there is at most one road between any two cities.
First print an integer $k$: the number of required roads.
Then, print $k$ lines that describe the new roads. You can print any valid solution.
- $1 \le n \le 10^5$
- $1 \le m \le 2 \cdot 10^5$
- $1 \le a,b \le n$