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dfs.py
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dfs.py
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#!/usr/bin/env python3
# -*- coding: utf-8 -*-
# Contributors:
# Artem Tabolin <[email protected]>
# dfs с восстановлением пути
def dfs(graph, u, visited=None, previous=None):
if visited is None:
visited = [False] * len(graph)
if previous is None:
previous = [None] * len(graph)
visited[u] = True
for v in graph[u]:
if not visited[v]:
previous[v] = u
dfs(graph, v, visited, previous)
return previous
def get_path(previous, u):
path = []
while previous[u] is not None:
path.append(u)
u = previous[u]
path.reverse()
return path
prev = dfs(graph, 0)
print(get_path(prev, 4))
print(get_path(prev, 2))
# Проверка на наличие циклов (неориентированный случай)
def dfs(graph, u, prev=None, visited=None):
if visited is None:
visited = [False] * len(graph)
visited[u] = True
for v in graph[u]:
if v != prev:
if visited[v]:
return True
else:
if dfs(graph, v, u, visited):
return True
return False
# Проверка на наличие циклов (ориентированный случай)
WHITE, GRAY, BLACK = 0, 1, 2
def dfs(graph, u, state=None):
if state is None:
state = [WHITE] * len(graph)
state[u] = GRAY
is_cyclic = False
for v in graph[u]:
if state[v] == GRAY:
is_cyclic = True
break
elif state[v] == WHITE:
if dfs(graph, v, state):
is_cyclic = True
break
# Можно сократить до:
# if state[v] == GRAY or state[v] == WHITE and dfs(graph, v, state):
# is_cyclic = True
# break
state[u] = BLACK
return is_cyclic