Learn Algorithm Design by Building a Shortest Path Algorithm - Step 45

Python
1

Tell us what’s happening:

I don’t have an issue. I just don’t understand why I need to add [-1] at this point of the code. What purpose does it serve? Is it an index?

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)

# User Editable Region

    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]
                if paths[node][-1] == node:
                    pass

# User Editable Region

    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 45

1 Like
2

Keep going to find out. -1 is the last element of a list

list = [1, 2, 3]
print(list[-1])  // outputs 3

TRY IT in a console or in your code you print things to see what it is.

1 Like