In C how do I output the set of back edges detected during D

In C++ how do I output the set of back edges detected during DFS?

Solution

#include<iostream>

#include <list>

#include <limits.h>

using namespace std;

class Graph

{

    int V;    // No. of vertices

    list<int> *adj;    // Pointer to an array containing adjacency lists

    bool isCyclicUtil(int v, bool visited[], bool *rs); // used by isCyclic()

public:

    Graph(int V);   // Constructor

    void addEdge(int v, int w);   // to add an edge to graph

    bool isCyclic();    // returns true if there is a cycle in this graph

};

Graph::Graph(int V)

{

    this->V = V;

    adj = new list<int>[V];

}

void Graph::addEdge(int v, int w)

{

    adj[v].push_back(w); // Add w to v’s list.

}

// This function is a variation of DFSUytil() in http://www.geeksforgeeks.org/archives/18212

bool Graph::isCyclicUtil(int v, bool visited[], bool *recStack)

{

    if(visited[v] == false)

    {

        // Mark the current node as visited and part of recursion stack

        visited[v] = true;

        recStack[v] = true;

        // Recur for all the vertices adjacent to this vertex

        list<int>::iterator i;

        for(i = adj[v].begin(); i != adj[v].end(); ++i)

        {

            if ( !visited[*i] && isCyclicUtil(*i, visited, recStack) )

                return true;

            else if (recStack[*i])

                return true;

        }

    }

    recStack[v] = false; // remove the vertex from recursion stack

    return false;

}

// Returns true if the graph contains a cycle, else false.

// This function is a variation of DFS() in http://www.geeksforgeeks.org/archives/18212

bool Graph::isCyclic()

{

    // Mark all the vertices as not visited and not part of recursion

    // stack

    bool *visited = new bool[V];

    bool *recStack = new bool[V];

    for(int i = 0; i < V; i++)

    {

        visited[i] = false;

        recStack[i] = false;

    }

    // Call the recursive helper function to detect cycle in different

    // DFS trees

    for(int i = 0; i < V; i++)

        if (isCyclicUtil(i, visited, recStack))

            return true;

    return false;

}

int main()

{

    // Create a graph given in the above diagram

    Graph g(4);

    g.addEdge(0, 1);

    g.addEdge(0, 2);

    g.addEdge(1, 2);

    g.addEdge(2, 0);

    g.addEdge(2, 3);

    g.addEdge(3, 3);

    if(g.isCyclic())

        cout << \"Graph contains cycle\";

    else

        cout << \"Graph doesn\'t contain cycle\";

    return 0;

}