Tree edge: 0 --> 2
Tree edge: 2 --> 1
Back edge: 1 --> 1
Tree edge: 1 --> 3
Back edge: 3 --> 1
Tree edge: 3 --> 4
Back edge: 4 --> 0
Back edge: 4 --> 1
Forward or cross edge: 2 --> 3
1 10
3 8
2 9
4 7
5 6
