Input:

16
1 7
2 7
3 7
7 8
8 9
9 10
9 11
9 12
3 15
4 15
5 15
15 16
4 6
6 13
6 14
-1 -1
3 3
1 4
2 5
4 2
5 2
-1 -1

Expected output:

Source nodes: 1 2 3 4 5

Similar node pairs: (3, 3) (1, 4) (2, 5) (4, 2) (5, 2) (8, 7) (9, 8) (10, 9) (11, 9) (12, 9) (7, 15) (15, 7), (16, 15) (6, 4), (13, 6) (14, 6) (16, 8) (8, 16)

Collapsed graph:

3: 3 14 16
14 16
3 16