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: Determine whether there is a path between two nodes in 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:

search_path(start=0, end=2) -> True
search_path(start=0, end=0) -> True
search_path(start=4, end=5) -> False

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
%load ../graph/graph.py



In [ ]:

    
def path_exists(start, end):
    # TODO: Implement me
    pass

Unit Test

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



In [ ]:

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


class TestPathExists(object):

    def test_path_exists(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)

        assert_equal(path_exists(nodes[0], nodes[2]), True)
        assert_equal(path_exists(nodes[0], nodes[0]), True)
        assert_equal(path_exists(nodes[4], nodes[5]), False)

        print('Success: test_path_exists')


def main():
    test = TestPathExists()
    test.test_path_exists()


if __name__ == '__main__':
    main()

Solution Notebook

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