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Fix mypy errors at bfs_shortest_path algo (#4572)

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Hasanul Islam 2021-07-27 14:09:17 +06:00 committed by GitHub
parent 6732fa0131
commit c5003a2c46
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1 changed files with 16 additions and 12 deletions
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28
graphs/breadth_first_search_shortest_path.py
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@ -3,6 +3,8 @@ from a given source node to a target node in an unweighted graph.
""" """
from __future__ import annotations from __future__ import annotations
from typing import Optional
graph = { graph = {
"A": ["B", "C", "E"], "A": ["B", "C", "E"],
"B": ["A", "D", "E"], "B": ["A", "D", "E"],
@ -15,17 +17,19 @@ graph = {
class Graph: class Graph:
def __init__(self, graph: dict[str, str], source_vertex: str) -> None: def __init__(self, graph: dict[str, list[str]], source_vertex: str) -> None:
"""Graph is implemented as dictionary of adjacency lists. Also, """
Graph is implemented as dictionary of adjacency lists. Also,
Source vertex have to be defined upon initialization. Source vertex have to be defined upon initialization.
""" """
self.graph = graph self.graph = graph
# mapping node to its parent in resulting breadth first tree # mapping node to its parent in resulting breadth first tree
self.parent = {} self.parent: dict[str, Optional[str]] = {}
self.source_vertex = source_vertex self.source_vertex = source_vertex
def breath_first_search(self) -> None: def breath_first_search(self) -> None:
"""This function is a helper for running breath first search on this graph. """
This function is a helper for running breath first search on this graph.
>>> g = Graph(graph, "G") >>> g = Graph(graph, "G")
>>> g.breath_first_search() >>> g.breath_first_search()
>>> g.parent >>> g.parent
@ -44,7 +48,8 @@ class Graph:
queue.append(adjacent_vertex) queue.append(adjacent_vertex)
def shortest_path(self, target_vertex: str) -> str: def shortest_path(self, target_vertex: str) -> str:
"""This shortest path function returns a string, describing the result: """
This shortest path function returns a string, describing the result:
1.) No path is found. The string is a human readable message to indicate this. 1.) No path is found. The string is a human readable message to indicate this.
2.) The shortest path is found. The string is in the form 2.) The shortest path is found. The string is in the form
`v1(->v2->v3->...->vn)`, where v1 is the source vertex and vn is the target `v1(->v2->v3->...->vn)`, where v1 is the source vertex and vn is the target
@ -64,17 +69,16 @@ class Graph:
'G' 'G'
""" """
if target_vertex == self.source_vertex: if target_vertex == self.source_vertex:
return f"{self.source_vertex}" return self.source_vertex
elif not self.parent.get(target_vertex):
target_vertex_parent = self.parent.get(target_vertex)
if target_vertex_parent is None:
return f"No path from vertex:{self.source_vertex} to vertex:{target_vertex}" return f"No path from vertex:{self.source_vertex} to vertex:{target_vertex}"
else:
return self.shortest_path(self.parent[target_vertex]) + f"->{target_vertex}" return self.shortest_path(target_vertex_parent) + f"->{target_vertex}"
if __name__ == "__main__": if __name__ == "__main__":
import doctest
doctest.testmod()
g = Graph(graph, "G") g = Graph(graph, "G")
g.breath_first_search() g.breath_first_search()
print(g.shortest_path("D")) print(g.shortest_path("D"))