topo_sorting.py

from collections import defaultdict


class Graph:
    def __init__(self, V):
        self.V = V
        self.graph = defaultdict(list)

    def addEdge(self, u, v):
        self.graph[u].append(v)

    def topologicalUtil(self, v, visited, stack):
        visited[v] = True
        for i in self.graph[v]:
            if visited[i] == False:
                self.topologicalUtil(i, visited, stack)
        stack.insert(0, v)      
    
    def topologicalSort(self):
        visited = [False] * self.V
        stack = []

        for i in range(self.V):
            if visited[i] == False:
                self.topologicalUtil(i, visited, stack)
            
        print(stack)

                
g = Graph(6)
g.addEdge(5, 2)
g.addEdge(5, 0)
g.addEdge(4, 0)
g.addEdge(4, 1)
g.addEdge(2, 3)
g.addEdge(3, 1)

print ("Following is a Topological Sort of the given graph")
g.topologicalSort()