Created
February 1, 2024 09:41
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Graph Theory Cycle Detector using DFS
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class Graph: | |
def __init__(self, vertices): | |
self.vertices = vertices | |
self.adj_list = {v: [] for v in vertices} | |
def add_edge(self, u, v): | |
self.adj_list[u].append(v) | |
self.adj_list[v].append(u) # for undirected graph | |
def has_cycle(graph): | |
visited = {v: False for v in graph.vertices} | |
parent = {v: None for v in graph.vertices} | |
def dfs_visit(node, parent_node): | |
visited[node] = True | |
parent[node] = parent_node | |
for neighbor in graph.adj_list[node]: | |
if not visited[neighbor]: | |
if dfs_visit(neighbor, node): | |
return True | |
elif parent_node != neighbor: | |
return True | |
return False | |
for vertex in graph.vertices: | |
if not visited[vertex]: | |
if dfs_visit(vertex, None): | |
return True | |
return False | |
vertices = ['A', 'B', 'C', 'D', 'E'] | |
edges = [('A', 'B'), ('B', 'C'), ('C', 'D'), ('D', 'E'), ('E', 'A')] # with a cycle | |
# edges = [('A', 'B'), ('B', 'C'), ('C', 'D'), ('D', 'E')] # without a cycle | |
graph = Graph(vertices) | |
for u, v in edges: | |
graph.add_edge(u, v) | |
if has_cycle(graph): | |
print("The graph contains a cycle.") | |
else: | |
print("The graph does not contain a cycle.") |
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