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Fix mypy errors at bfs_zero_one_shortest_path (#4521)

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Hasanul Islam 2021-07-02 17:52:26 +06:00 committed by GitHub
parent 62d4418851
commit 86baec0bc9
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1 changed files with 10 additions and 6 deletions
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graphs/bfs_zero_one_shortest_path.py
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@ -1,6 +1,7 @@
from collections import deque from collections import deque
from collections.abc import Iterator
from dataclasses import dataclass from dataclasses import dataclass
from typing import Iterator, List from typing import Optional, Union
""" """
Finding the shortest path in 0-1-graph in O(E + V) which is faster than dijkstra. Finding the shortest path in 0-1-graph in O(E + V) which is faster than dijkstra.
@ -21,7 +22,7 @@ class AdjacencyList:
"""Graph adjacency list.""" """Graph adjacency list."""
def __init__(self, size: int): def __init__(self, size: int):
self._graph: List[List[Edge]] = [[] for _ in range(size)] self._graph: list[list[Edge]] = [[] for _ in range(size)]
self._size = size self._size = size
def __getitem__(self, vertex: int) -> Iterator[Edge]: def __getitem__(self, vertex: int) -> Iterator[Edge]:
@ -58,7 +59,7 @@ class AdjacencyList:
self._graph[from_vertex].append(Edge(to_vertex, weight)) self._graph[from_vertex].append(Edge(to_vertex, weight))
def get_shortest_path(self, start_vertex: int, finish_vertex: int) -> int: def get_shortest_path(self, start_vertex: int, finish_vertex: int) -> Optional[int]:
""" """
Return the shortest distance from start_vertex to finish_vertex in 0-1-graph. Return the shortest distance from start_vertex to finish_vertex in 0-1-graph.
1 1 1 1 1 1
@ -106,18 +107,21 @@ class AdjacencyList:
ValueError: No path from start_vertex to finish_vertex. ValueError: No path from start_vertex to finish_vertex.
""" """
queue = deque([start_vertex]) queue = deque([start_vertex])
distances = [None for i in range(self.size)] distances: list[Union[int, None]] = [None] * self.size
distances[start_vertex] = 0 distances[start_vertex] = 0
while queue: while queue:
current_vertex = queue.popleft() current_vertex = queue.popleft()
current_distance = distances[current_vertex] current_distance = distances[current_vertex]
if current_distance is None:
continue
for edge in self[current_vertex]: for edge in self[current_vertex]:
new_distance = current_distance + edge.weight new_distance = current_distance + edge.weight
dest_vertex_distance = distances[edge.destination_vertex]
if ( if (
distances[edge.destination_vertex] is not None isinstance(dest_vertex_distance, int)
and new_distance >= distances[edge.destination_vertex] and new_distance >= dest_vertex_distance
): ):
continue continue
distances[edge.destination_vertex] = new_distance distances[edge.destination_vertex] = new_distance