2.2 KiB
id, title, challengeType, dashedName
| id | title | challengeType | dashedName |
|---|---|---|---|
| 65579228c669fcbebffd01d5 | Step 52 | 20 | step-52 |
--description--
The other bug is subtle. When a shorter distance is found for a neighbor node, paths[current] gets assigned to the neighbor node path, paths[node].
This means both variables point to the same list. Since lists are mutable, when you append the neighbor node to its path, both paths[node] and paths[current] are modified because they are the same list. This results in wrong paths, although the distances are correct.
You can fix that bug by assigning a copy of paths[current] to the neighbor node path. For that you can use the slice syntax:
my_list[:]
Where my_list is the list you want to copy. Modify the existing paths[node] = paths[current] assignment inside your if block by slicing paths[current].
--hints--
You should assign paths[current][:] to the neighbor node path.
({ test: () => assert.match(code, /^(\s*)if\s+paths\s*\[\s*node\s*\]\s+and\s+paths\s*\[\s*node\s*\]\s*\[\s*-\s*1\s*\]\s*==\s*node\s*:\s*^\1\s{4}paths\s*\[\s*node\s*\]\s*=\s*paths\s*\[\s*current\s*\]\s*\[\s*::?\s*\]/ms) })
--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)]
}
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]
--fcc-editable-region--
if paths[node] and paths[node][-1] == node:
paths[node] = paths[current]
--fcc-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')