Detect a cycle in directed graph using DFS

'''
Maintain 3 elements in the visited array, -1 means fresh and never visited, 0 means it is in the loop
so we should not get any 0 node while visiting and once you are done with the node, make it 1 means all
the neighbors have been visited.
'''
from collections import deque, defaultdict
def dfs(i,graph,visited):
    visited[i]=0
    for neigh in graph[i]:
        if visited[neigh]==0:
            return True
        if dfs(neigh,graph,visited):
            return True
    visited[i]=1
    return False

class Solution:
    def isCyclic(self, v, edges):
        graph=defaultdict(list)
        for a,b in edges:
            graph[a].append(b)
        visited=[-1]*v
        for i in range(v):
            if visited[i]==-1:
                if dfs(i,graph,visited):
                    return True
        return False