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Python Program for Detect Cycle in a Directed Graph
In this article, we will learn about the solution to the problem statement given below.
Problem statement − We are given a directed graph, we need to check whether the graph contains a cycle or not. The output should be true if the given graph contains at least one cycle, otherwise false.
Now let’s observe the solution in the implementation below −
Example
# collections module
from collections import defaultdict
# class for creation of graphs
class Graph():
# constructor
def __init__(self, vertices):
self.graph = defaultdict(list)
self.V = vertices
def addEdge(self, u, v):
self.graph[u].append(v)
def isCyclicUtil(self, v, visited, recStack):
# Marking current node visited and addition to recursion stack
visited[v] = True
recStack[v] = True
# if any neighbour is visited and in recStack then graph is cyclic in nature
for neighbour in self.graph[v]:
if visited[neighbour] == False:
if self.isCyclicUtil(neighbour, visited, recStack) == True:
return True
elif recStack[neighbour] == True:
return True
# pop the node after the end of recursion
recStack[v] = False
return False
# Returns true if graph is cyclic
def isCyclic(self):
visited = [False] * self.V
recStack = [False] * self.V
for node in range(self.V):
if visited[node] == False:
if self.isCyclicUtil(node, visited, recStack) == True:
return True
return False
g = Graph(4)
g.addEdge(0, 3)
g.addEdge(0, 2)
g.addEdge(3, 2)
g.addEdge(2, 0)
g.addEdge(1, 3)
g.addEdge(2, 1)
if g.isCyclic() == 1:
print ("Graph is cyclic in nature")
else:
print ("Graph is non-cyclic in nature")Output
Graph is cyclic in nature
All the variables are declared in the local scope and their references are seen in the figure above.
Conclusion
In this article, we have learned about how we can make a Python Program to Detect Cycle in a Directed Graph
Updated on: 20-Dec-2019
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