This notebook was prepared by [Donne Martin](https://github.com/donnemartin). Source and license info is on [GitHub](https://github.com/donnemartin/interactive-coding-challenges).

Challenge Notebook

Problem: Implement breadth-first search on a graph.

Constraints
Test Cases
Algorithm
Code
Unit Test
Solution Notebook

Constraints

Is the graph directed?
- Yes
Can we assume we already have Graph and Node classes?
- Yes

Test Cases

Input:

add_edge(source, destination, weight)

graph.add_edge(0, 1, 5)
graph.add_edge(0, 4, 3)
graph.add_edge(0, 5, 2)
graph.add_edge(1, 3, 5)
graph.add_edge(1, 4, 4)
graph.add_edge(2, 1, 6)
graph.add_edge(3, 2, 7)
graph.add_edge(3, 4, 8)

Result:

Order of nodes visited: [0, 1, 4, 5, 3, 2]

Algorithm

Refer to the Solution Notebook. If you are stuck and need a hint, the solution notebook's algorithm discussion might be a good place to start.

Code



In [ ]:

    
%run ../graph/graph.py



In [ ]:

    
def bfs(root, visit_func):
    # TODO: Implement me
    pass

Unit Test

The following unit test is expected to fail until you solve the challenge.



In [ ]:

    
%run ../utils/results.py



In [ ]:

    
# %load test_bfs.py
from nose.tools import assert_equal


class TestBfs(object):

    def __init__(self):
        self.results = Results()

    def test_bfs(self):
        nodes = []
        graph = Graph()
        for id in range(0, 6):
            nodes.append(graph.add_node(id))
        graph.add_edge(0, 1, 5)
        graph.add_edge(0, 4, 3)
        graph.add_edge(0, 5, 2)
        graph.add_edge(1, 3, 5)
        graph.add_edge(1, 4, 4)
        graph.add_edge(2, 1, 6)
        graph.add_edge(3, 2, 7)
        graph.add_edge(3, 4, 8)
        bfs(nodes[0], self.results.add_result)
        assert_equal(str(self.results), "[0, 1, 4, 5, 3, 2]")

        print('Success: test_bfs')


def main():
    test = TestBfs()
    test.test_bfs()


if __name__ == '__main__':
    main()

Solution Notebook

Review the Solution Notebook for a discussion on algorithms and code solutions.