def dijkstra(graph: Graph, start_node, end_node) -> (int, List):
"""
Dijkstras shortest path algorithm implementation
Works for directed and undirected graphs with non negative weights
Time complexity: O(EV + V^2 * logV)
:return Returns a tuple of the distance of the shortest path and the nodes to reach the shortest path
"""
# Min heap
pq = FibonacciHeap()
pq.insert((0, start_node))
# Final distances and paths from the start node
distances = {key: sys.maxsize for key in graph.get_vertices()}
paths = {key: [] for key in graph.get_vertices()}
# Finished nodes
visited_nodes = set()
# Set start node distance to 0
distances[start_node] = 0
while not pq.is_empty():
distance, vertex = pq.pop()
if distance == sys.maxsize or end_node in visited_nodes:
# Only unconnected vertices are left or we found the minimal distance
break
for outgoing_edge in graph.get_outgoing_edges(vertex):
next_vertex = outgoing_edge.a if outgoing_edge.a != vertex else outgoing_edge.b
if next_vertex in visited_nodes:
continue
if distance + outgoing_edge.weight < distances[next_vertex]:
distances[next_vertex] = distance + outgoing_edge.weight
paths[next_vertex] = paths[vertex] + [next_vertex]
pq.insert((distance + outgoing_edge.weight, next_vertex))
visited_nodes.add(vertex)
return distances[end_node], paths[end_node]
def dijkstra(graph: Graph, start_node, end_node) -> (int, List):
"""
Dijkstras shortest path algorithm implementation
Works for directed and undirected graphs with non negative weights
Time complexity: O(EV + V^2 * logV)
:return Returns a tuple of the distance of the shortest path and the nodes to reach the shortest path
"""
# Min heap
pq = FibonacciHeap()
pq.insert((0, start_node))
# Final distances and paths from the start node
distances = {key: sys.maxsize for key in graph.get_vertices()}
paths = {key: [] for key in graph.get_vertices()}
# Finished nodes
visited_nodes = set()
# Set start node distance to 0
distances[start_node] = 0
while not pq.is_empty():
distance, vertex = pq.pop()
if distance == sys.maxsize or end_node in visited_nodes:
# Only unconnected vertices are left or we found the minimal distance
break
for outgoing_edge in graph.get_outgoing_edges(vertex):
next_vertex = outgoing_edge.a if outgoing_edge.a != vertex else outgoing_edge.b
if next_vertex in visited_nodes:
continue
if distance + outgoing_edge.weight < distances[next_vertex]:
distances[next_vertex] = distance + outgoing_edge.weight
paths[next_vertex] = paths[vertex] + [next_vertex]
pq.insert((distance + outgoing_edge.weight, next_vertex))
visited_nodes.add(vertex)
return distances[end_node], paths[end_node]
def floyd_warshal(g: Graph):
"""
the Floyd–Warshall algorithm is an algorithm for finding shortest paths in a weighted graph with positive
or negative edge weights (but with no negative cycles). A single execution of the algorithm will find the
lengths (summed weights) of the shortest paths between all pairs of vertices, though it does not return details
of the paths themselves.
Time complexity: O(V^3)
"""
vertices_mapping = dict(zip(g.get_vertices(), count()))
# Build V*V matrix initialized to sys.maxsize
matrix = [[sys.maxsize] * len(vertices_mapping) for _ in range(len(vertices_mapping))]
# Set distance to itself to zero
for vertex in g.get_vertices():
matrix[vertices_mapping[vertex]][vertices_mapping[vertex]] = 0
# Set distance for all edges
for vertex in g.get_vertices():
for edge in g.get_outgoing_edges(vertex):
succesive_vertex = edge.a if edge.a != vertex else edge.b
matrix[vertices_mapping[vertex]][vertices_mapping[succesive_vertex]] = edge.weight
# Main loop
for k in g.get_vertices():
for i in g.get_vertices():
for j in g.get_vertices():
matrix[vertices_mapping[i]][vertices_mapping[j]] = min(matrix[vertices_mapping[i]][vertices_mapping[k]] + \
matrix[vertices_mapping[k]][vertices_mapping[j]], matrix[vertices_mapping[i]][vertices_mapping[j]])
return [(a, b, matrix[vertices_mapping[a]][vertices_mapping[b]]) for a in g.get_vertices() for b in g.get_vertices() if
matrix[vertices_mapping[a]][vertices_mapping[b]] != sys.maxsize]
def floyd_warshal(g: Graph):
"""
the Floyd–Warshall algorithm is an algorithm for finding shortest paths in a weighted graph with positive
or negative edge weights (but with no negative cycles). A single execution of the algorithm will find the
lengths (summed weights) of the shortest paths between all pairs of vertices, though it does not return details
of the paths themselves.
Time complexity: O(V^3)
"""
vertices_mapping = dict(zip(g.get_vertices(), count()))
# Build V*V matrix initialized to sys.maxsize
matrix = [[sys.maxsize] * len(vertices_mapping)
for _ in range(len(vertices_mapping))]
# Set distance to itself to zero
for vertex in g.get_vertices():
matrix[vertices_mapping[vertex]][vertices_mapping[vertex]] = 0
# Set distance for all edges
for vertex in g.get_vertices():
for edge in g.get_outgoing_edges(vertex):
succesive_vertex = edge.a if edge.a != vertex else edge.b
matrix[vertices_mapping[vertex]][
vertices_mapping[succesive_vertex]] = edge.weight
# Main loop
for k in g.get_vertices():
for i in g.get_vertices():
for j in g.get_vertices():
matrix[vertices_mapping[i]][vertices_mapping[j]] = min(matrix[vertices_mapping[i]][vertices_mapping[k]] + \
matrix[vertices_mapping[k]][vertices_mapping[j]], matrix[vertices_mapping[i]][vertices_mapping[j]])
return [(a, b, matrix[vertices_mapping[a]][vertices_mapping[b]])
for a in g.get_vertices() for b in g.get_vertices()
if matrix[vertices_mapping[a]][vertices_mapping[b]] != sys.maxsize]