Learn Algorithm Design by Building a Shortest Path Algorithm - Step 47

Python
1

Tell us what’s happening:

Describe your issue in detail here.

I have tried multiple multiple ways, have seen feedback from others and what people gave as hints but still can’t understand what’s the answer…

Your code so far

my_graph = {
    'A': [('B', 3), ('D', 1)],
    'B': [('A', 3), ('C', 4)],
    'C': [('B', 4), ('D', 7)],
    'D': [('A', 1), ('C', 7)]
}

def shortest_path(graph, start):
    unvisited = list(graph)
    distances = {node: 0 if node == start else float('inf') for node in graph}
    paths = {node: [] for node in graph}
    paths[start].append(start)
    
    while unvisited:
        current = min(unvisited, key=distances.get)
        for node, distance in graph[current]:
            if distance + distances[current] < distances[node]:
                distances[node] = distance + distances[current]

# User Editable Region

                if paths[node] and paths[node][-1] == node:
                    paths[node] = paths[current]
                    

# User Editable Region

                else:
                    paths[node].extend(paths[current])
                paths[node].append(node)
        unvisited.remove(current)
    
    print(f'Unvisited: {unvisited}\nDistances: {distances}\nPaths: {paths}')
    
shortest_path(my_graph, 'A')

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Challenge Information:

Learn Algorithm Design by Building a Shortest Path Algorithm - Step 47

2

You appear to have created this post without editing the template. Please edit your post to Tell us what’s happening in your own words.

3

What have you tried?

You need to create a new list by using a complete slice of the old list:

new_list = old_list[:]

https://therenegadecoder.com/code/how-to-clone-a-list-in-python/#copy-a-list-using-a-slice

https://www.geeksforgeeks.org/python-cloning-copying-list/

If you leave it like this:

paths[node] = paths[current]

They both refer to the same list in memory and changes to one will affect both.

4

I found the solution but I still did not understand much…

1 Like
5

Did you read this?
https://therenegadecoder.com/code/how-to-clone-a-list-in-python/#problem-introduction

6

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