freeCodeCamp/curriculum/challenges/german/07-scientific-computing-with-python/learn-algorithm-design-by-building-a-shortest-path-algorithm/6557924d47c325bf27afbe51.md

id, title, challengeType, dashedName

id	title	challengeType	dashedName
6557924d47c325bf27afbe51	Step 53	20	step-53

--description--

The algorithm is complete but you can improve the output. Also, you can provide the function with an additional argument to return only the path between two nodes.

Add target as the third parameter to your function declaration and give it the default value of an empty string.

--hints--

Your function should take three parameters:graph, start, and target. The order matters.

({ test: () => assert.match(code, /^def\s+shortest_path\s*\(\s*graph\s*,\s*start\s*,\s*target\s*=?\s*.*\s*\)\s*:/m) })

The target parameter should have the default value of an empty string.

({ test: () => assert(runPython(`
    import inspect
    sig = str(inspect.signature(shortest_path))
    sig == "(graph, start, target='')"
  `))
})

--seed--

--seed-contents--

my_graph = {
    'A': [('B', 3), ('D', 1)],
    'B': [('A', 3), ('C', 4)],
    'C': [('B', 4), ('D', 7)],
    'D': [('A', 1), ('C', 7)]
}
--fcc-editable-region--
def shortest_path(graph, start):
--fcc-editable-region--
    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]
                if paths[node] and paths[node][-1] == node:
                    paths[node] = paths[current][:]
                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')