Output without isolates:
# 0
1
2
# 1
2
3
# 2
4
# 3
4

Output with isolates:
# 0
1
2
# 1
2
3
# 2
4
# 3
4
# 5
# 6

Output vertex and edge labels:
# A
B 1
C 4
# B
C 3
D 2
# C
E 5
# D
E 6