Detect whether the graph has a cycle, and find the longest cycle.

dfsGraph.py

from collections import defaultdict
class Graph:
  def __init__(self):
    self.graph=defaultdict(list)
    self.V=len(self.graph)
    
  def addEdge(self, u, v):
    self.graph[u].append(v)
    self.V=len(self.graph)
    
  def DFSUtil(self, v, visited):
    visited[v]=True
    hasC=False
    print(v)
    
    for i in self.graph[v]:
      if visited[i]==False:
        self.DFSUtil(i, visited)

  def noVertices(self):
    return self.V
  
  def isCyclicUtil(self, v, visited, recStack):
      visited[v] = True
      recStack[v] = True
      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
      recStack[v] = False
      return False

  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
    
        
  def DFS(self, v):
    visited =[False] * (len(self.graph))
    self.DFSUtil(v, visited)
    
g=Graph()
g.addEdge(0, 1)
g.addEdge(0, 2)
g.addEdge(1, 2)
g.addEdge(2, 0)
g.addEdge(2, 3)
g.addEdge(3, 3)


g.DFS(0)
print("no of verticesis:", g.noVertices())

if (g.isCyclic()):
  print("Cycle detected")
else:
  print("No cycle detected")