If you're doing a greedy solution and you're sorting by the rightmost endpoints (B_i), you need to sort with the leftmost endpoints as second key. That is, if B_i == B_j, the shortest segment of i and j goes first in the list.

This basically means that longer segments are kept, so for inputs:

3
3 5
1 5
5 6

You would get result
2
1 5
5 6

instead of
2
3 5
5 6

which means you get a bigger covering of the set but the problem statement didn't mention this requirement.

Edited by author 24.12.2014 21:07

there is no such information in statement