def shortest_path(source, target):
"""
Returns the shortest list of (movie_id, person_id) pairs
that connect the source to the target.
If no possible path, returns None.
"""
frontier = QueueFrontier()
explored = []
source_node = Node(source, None, None)
frontier.add(source_node)
while not frontier.empty():
node = frontier.remove()
if node.person == target:
return find_path(node)
else:
explored.append(node.person)
for movie, person in neighbors_for_person(node.person):
if not frontier.contains_person(person) and person not in explored:
child = Node(person, node, movie)
frontier.add(child)
return None
def shortest_path(source, target):
"""
Returns the shortest list of (movie_id, person_id) pairs
that connect the source to the target.
If no possible path, returns None.
"""
frontier = QueueFrontier()
start = Node(source, None, None)
explored = set()
frontier.add(start)
while True:
if frontier.empty():
return None # Frontier empty; no solution possible
nextNode = frontier.remove() # Fetch the next node to search through
explored.add(
nextNode) # Add the node to the already explored nodes set
neighbors = neighbors_for_person(nextNode.person)
for movie, person in neighbors:
if person == target:
movies, people = [], []
while nextNode.parent is not None:
movies.append(nextNode.movie)
people.append(nextNode.person)
nextNode = nextNode.parent # Going up a level in node parent list
movies.reverse(
) # Reversing movies list because append() appends new item at the end of the list, and we are going from end back to the starting.
people.reverse(
) # So, we basically need the new elements to be appended at the stating. This is a clever way to get the correct result.
solution = (
movies, people
) # Need to assign it to a variable so the data type becomes a tuple
return solution
elif frontier.contains_person(person) and person not in explored:
newNode = Node(person, nextNode, movie)
frontier.add(newNode)