I've just got AC but with another solution. But I wonder, what is #12test?
I tried:
inp:
2
1 2
2 1
outp:
1
1 2
//------
inp:
0
outp:
0
PS I know, this test is incorrect.
//------
inp:
4
1 4
2 8
3 6
5 7
outp:
2
1 4
5 7

First time I use list of segments. Algo:
-find segment with max intersections
-delete it from list
And I do it while segment with max intersections have more then 0 intersections. Is it algo wrong?
PS Sorry for my english.

I used the same algo and got WA12.
I think this test is:
5
3 6
7 8
1 2
0 4
5 9
Answer:
3
1 2
3 6
7 8