Update minmax.py

[adikele]

The function for finding the Minimum Spanning Tree (mst) in the minmax file seems to be in error: one of the edges is displayed twice in the mst.

I have rewritten the function for finding the mst and deleted the earlier one; the edges are now correctly displayed. Additionally, the weight of the mst is also displayed.

The MinSpanningTree branch contains this rewritten function in place of the original mst function. The difference between the output of the functions in the two versions is demonstrated with the help of an example:

g = graph()

g.add_node('A')
g.add_node('B')
g.add_node('C')
g.add_node('D')
g.add_node('E')

g.add_edge(('A', 'C'), 10, 'AC')
g.add_edge(('A', 'D'), 7, 'AD')
g.add_edge(('B', 'D'), 32, 'BD')
g.add_edge(('C', 'D'), 9, 'CD')
g.add_edge(('D', 'E'), 23, 'DE')

using the current function:{'A': 'D', 'C': 'D', 'B': 'D', 'E': 'D', 'D': 'B'}

using the new function in MinSpanningTree branch [('A', 'D'), ('D', 'C'), ('D', 'E'), ('D', 'B'), 71]

[adikele]

In unittests-minmax.py, I have rewritten the tree_weight function so that it can also accept a list of tuples.
EDIT: unittests-minmax.py has been reverted to its original state.
Instead, in minmax.py, the minimum spanning tree is now returned as a dictionary