89 lines
2.4 KiB
Python
89 lines
2.4 KiB
Python
"""
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Breadth-first search and depth-first search.
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Author: Wenru Dong
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"""
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from typing import List, Optional, Generator, IO
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from collections import deque
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class Graph:
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"""Undirected graph."""
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def __init__(self, num_vertices: int):
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self._num_vertices = num_vertices
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self._adjacency = [[] for _ in range(num_vertices)]
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def add_edge(self, s: int, t: int) -> None:
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self._adjacency[s].append(t)
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self._adjacency[t].append(s)
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def _generate_path(self, s: int, t: int, prev: List[Optional[int]]) -> Generator[str, None, None]:
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if prev[t] or s != t:
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yield from self._generate_path(s, prev[t], prev)
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yield str(t)
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def bfs(self, s: int, t: int) -> IO[str]:
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"""Print out the path from Vertex s to Vertex t
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using bfs.
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"""
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if s == t: return
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visited = [False] * self._num_vertices
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visited[s] = True
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q = deque()
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q.append(s)
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prev = [None] * self._num_vertices
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while q:
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v = q.popleft()
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for neighbour in self._adjacency[v]:
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if not visited[neighbour]:
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prev[neighbour] = v
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if neighbour == t:
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print("->".join(self._generate_path(s, t, prev)))
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return
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visited[neighbour] = True
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q.append(neighbour)
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def dfs(self, s: int, t: int) -> IO[str]:
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"""Print out a path from Vertex s to Vertex t
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using dfs.
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"""
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found = False
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visited = [False] * self._num_vertices
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prev = [None] * self._num_vertices
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def _dfs(from_vertex: int) -> None:
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nonlocal found
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if found: return
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visited[from_vertex] = True
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if from_vertex == t:
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found = True
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return
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for neighbour in self._adjacency[from_vertex]:
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if not visited[neighbour]:
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prev[neighbour] = from_vertex
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_dfs(neighbour)
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_dfs(s)
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print("->".join(self._generate_path(s, t, prev)))
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if __name__ == "__main__":
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graph = Graph(8)
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graph.add_edge(0, 1)
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graph.add_edge(0, 3)
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graph.add_edge(1, 2)
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graph.add_edge(1, 4)
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graph.add_edge(2, 5)
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graph.add_edge(3, 4)
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graph.add_edge(4, 5)
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graph.add_edge(4, 6)
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graph.add_edge(5, 7)
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graph.add_edge(6, 7)
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graph.bfs(0, 7)
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graph.dfs(0, 7)
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