graph.cpp

/*
 * graph.cpp
 *
 *  Created on: Nov 14, 2013
 *      Author: olga
 */

#include "graph.h"
#include <iostream>
#include <list>
#include <limits.h>

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 vÕs list.
}

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.
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;
}