detect_cycle_directed_graph

class Graph:
    def __init__(self, v):
        # No. of vertices of graph
        self.v = v
        # Adjacency List
        self.adj = [0] * v
        for i in range(self.v):
            self.adj[i] = []

    def addedge(self, i,j):
        self.adj[i].append(j)

    def isCyclic(self):
        visited = [False] * self.v
        helper = [False] * self.v
        for i in range(self.v):
            if visited[i] == False:
                ans = self.DFS(i,visited,helper)
                if ans == True:
                    return True
        return False


    def DFS(self,i, visited,helper):
        visited[i] = True
        helper[i] = True
        neighbours = self.adj[i]
        for k in range(len(neighbours)):
            curr = neighbours[k]
            if helper[curr] == True:
                return True
            if visited[curr] == False:
                ans = self.DFS(curr,visited,helper)
                if ans == True:
                    return True
        helper[i] = False
        return False


if __name__ == "__main__":
    # No of nodes
    n = 4
    g = Graph(n)

    g.addedge(0, 1)
    g.addedge(3, 1)
    g.addedge(1, 2)
    g.addedge(0, 3)

if g.isCyclic() == 1:
    print("Graph has a cycle")
else:
    print("Graph has no cycle")