Question

How should I proceed on doing this?
This IS a homework, and I’m having a huge problem with it.
Now, the issue is that I must not use libs.

I have a graph like:

{'A': {'C': 2, 'B': 10}, 'C': {'B': 7, 'D': 2}, 'B': {}, 'D': {'A': 5, 'B': 4}}

using dictionaries, taken from a file.

I am using the algorithm at http://www.python.org/doc/essays/graphs/ to find all the paths, so there is no problem there.

But now that I have all the paths from one point to another, I need to sum the weights and get the complete cost on it.

If you could help me, and direct me on some good ways to approach it, I would appreciate it.

Answer 1

gr = {'A': {'C': 2, 'B': 10},
      'C': {'B': 7, 'D': 2},
      'B': {'E': 2},
      'D': {'A': 5, 'B': 4, 'E': 3}
      'E': {}}

def paths(gr, frm, to, path_len=0, visited=None):

    if frm == to:
        return [[to, path_len]]

    visited = visited or []
    result = []
    for point, length in gr[frm].iteritems():
        if point in visited:
            continue
        visited.append(point)
        for sub_path in paths(gr, point, to, path_len + length, visited[:]):
            result.append([frm] + sub_path)

    return result

>>> print paths(gr, 'A', 'E')
[['A', 'C', 'B', 'E', 11], ['A', 'C', 'D', 'E', 7], ['A', 'B', 'E', 12]]