def bfs(road_network, s_vid, e_vid):
"""
Return the path from vertex s_vid to vertex e_vid using Dijkstra's algorithm.
The implementation is the same as the function is_reachable(), except that instead of bool type, we return a Path
found by Breadth First Search.
:param road_network: RoadNetwork
:param s_vid: int
:param e_vid: int
:return: Path
"""
frontier = Queue()
frontier.put(s_vid)
came_from = dict()
came_from[s_vid] = None
while not frontier.empty():
current = frontier.get()
if current == e_vid:
break
for neighbor in road_network.get_neighbors(current):
if neighbor not in came_from:
frontier.put(neighbor)
came_from[neighbor] = current
return construct_path(road_network, s_vid, e_vid, came_from)
def is_reachable(road_network, s_vid, e_vid):
"""
Return True if there exist a path from s_vid to e_vid, otherwise return False.
The algorithm is basic Breadth-First-Search (with early exit).
:param road_network: RoadNetwork
:param s_vid: int
:param e_vid: int
:return: bool
"""
frontier = Queue()
frontier.put(s_vid)
came_from = dict()
came_from[s_vid] = None
while not frontier.empty():
current = frontier.get()
if current == e_vid:
return True
for neighbor in road_network.get_neighbors(current):
if neighbor not in came_from:
frontier.put(neighbor)
came_from[neighbor] = current
return False
