Topological Sorting

#include <cstdio>
#include <vector>
#include <list>
#include <cstring>

using namespace std;

// Class to represent a Digraph, with vertices labeled
// from 0 to V-1, where V is the number of vertices
class Graph {
private:
    int V;
    vector <int>* adjList;
    bool* explored;
    list <int> topologicalOrder;

    void dfsUtil(int u) {
        explored[u] = true;
        for (vector <int>::iterator v = adjList[u].begin(); v != adjList[u].end(); v++)
            if (!explored[*v])
                dfsUtil(*v);
        topologicalOrder.push_front(u);
    }

    void dfs()    {
        for (int u = 0; u < V; u++)
            if (!explored[u])
                dfsUtil(u);
    }

public:

    // create an empty Digraph having V vertices
    Graph(int V) {
        this->V = V;
        adjList = new vector <int>[V];
        explored = new bool[V];
        memset(explored, false, V * sizeof(bool));
    }

    ~Graph()    {
        delete [] adjList;
        delete [] explored;
    }

    // add a directed edge u -> v to the digraph
    // returns false if either u or v is less than 0 or greater than equal to V
    // returns true if the edge was added to the digraph
    bool addEdge(int u, int v)  {
        if (u < 0 || u >= V) return false;
        if (v < 0 || v >= V) return false;
        adjList[u].push_back(v);
        return true;
    }

    list <int> getTopologicalOrder()    {
        if (topologicalOrder.empty())
            dfs();

        return topologicalOrder;
    }

    void printTopologicalOrder()    {
        if (topologicalOrder.empty())
            dfs();

        printf("Topological Order :");
        for (list<int>::iterator it = topologicalOrder.begin(); it != topologicalOrder.end(); it++)
            printf(" %d", *it);
        printf("\n");
    }

};

int main() {
    Graph G(8);

    G.addEdge(2, 0);
    G.addEdge(1, 2);
    G.addEdge(2, 3);
    G.addEdge(2, 5);
    G.addEdge(6, 2);
    G.addEdge(7, 5);
    G.addEdge(4, 7);
    G.addEdge(6, 7);
    G.addEdge(4, 3);

    G.printTopologicalOrder();

    return 0;
}