topological_sorting.cpp

// C++ program to print topological sorting of a DAG

#include <iostream>
#include <list>
#include <stack>
using namespace std;

class Graph {
	int V;

	list<int>* adj;

	void topologicalSortUtil(int v, bool visited[],
							stack<int>& Stack);

public:
	Graph(int V);

	void addEdge(int v, int w);

	void topologicalSort();
};

Graph::Graph(int V)
{
	this->V = V;
	adj = new list<int>[V];
}

void Graph::addEdge(int v, int w)
{
	adj[v].push_back(w);
}

void Graph::topologicalSortUtil(int v, bool visited[],
								stack<int>& Stack)
{
	visited[v] = true;

	list<int>::iterator i;
	for (i = adj[v].begin(); i != adj[v].end(); ++i)
		if (!visited[*i])
			topologicalSortUtil(*i, visited, Stack);

	Stack.push(v);
}

void Graph::topologicalSort()
{
	stack<int> Stack;

	bool* visited = new bool[V];
	for (int i = 0; i < V; i++)
		visited[i] = false;

	for (int i = 0; i < V; i++)
		if (visited[i] == false)
			topologicalSortUtil(i, visited, Stack);

	while (Stack.empty() == false) {
		cout << Stack.top() << " ";
		Stack.pop();
	}
}

int main()
{
	Graph g(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);

	cout << "Following is a Topological Sort of the given "
			"graph \n";

	g.topologicalSort();

	return 0;
}