It seems, saving 'explored' in a set returns wrong results. During traversal, the order of the entries in var 'explored' are changed by python (by version 2 AND 3).

Result during iteration with data type 'set':

set(['A', 'B'])
set(['A', 'C', 'B'])
set(['A', 'C', 'B', 'D'])
set(['A', 'C', 'B', 'E', 'D'])
set(['A', 'C', 'B', 'E', 'D', 'F'])
set(['A', 'C', 'B', 'E', 'D', 'F'])

For comparison, here's the result with data type 'list':

['A', 'B']
['A', 'B', 'C']
['A', 'B', 'C', 'D']
['A', 'B', 'C', 'D', 'E']
['A', 'B', 'C', 'D', 'E', 'F']
['A', 'B', 'C', 'D', 'E', 'F']

The result is for the old example-graph essentially the same, but for more complex graphs it will be wrong.

I added a slightly more complex graph:

G = {
    "A": ["B", "E", "C"],
    "B": ["A", "F", "C"],
    "C": ["A", "B", "E", "I", "H"],
    "D": ["F"],
    "E": ["A", "C"],
    "F": ["G", "D", "B"],
    "G": ["F"],
    "H": ["I", "C"],
    "I": ["H", "C"]
}

Here's the wrong result with data type 'set' - note how the order changes:

set(['A', 'B'])
set(['A', 'B', 'E'])
set(['A', 'C', 'B', 'E'])
set(['A', 'C', 'B', 'E', 'F'])
set(['A', 'C', 'B', 'E', 'F', 'I'])
set(['A', 'C', 'B', 'E', 'F', 'I', 'H'])
set(['A', 'C', 'B', 'E', 'G', 'F', 'I', 'H'])
set(['A', 'C', 'B', 'E', 'D', 'G', 'F', 'I', 'H'])
set(['A', 'C', 'B', 'E', 'D', 'G', 'F', 'I', 'H'])

What should be the result? (order of vertices on every level does not matter)

Level 0: A
Level 1: B,C,E
Level 2: F,I,H
Level 3: G,D

If you take a close look above, e.g. D is returned on the wrong level.

Here's the correct result with data type 'list':

['A', 'B']
['A', 'B', 'E']
['A', 'B', 'E', 'C']
['A', 'B', 'E', 'C', 'F']
['A', 'B', 'E', 'C', 'F', 'I']
['A', 'B', 'E', 'C', 'F', 'I', 'H']
['A', 'B', 'E', 'C', 'F', 'I', 'H', 'G']
['A', 'B', 'E', 'C', 'F', 'I', 'H', 'G', 'D']
['A', 'B', 'E', 'C', 'F', 'I', 'H', 'G', 'D']

I suggest to include the more complex graph for testing purposes.

• Add an algorithm?
• [x ] Fix a bug or typo in an existing algorithm?
• Documentation change?