find bridges in a graph

// A C++ program to find bridges in a given undirected graph
#include<bits/stdc++.h>
#include <list>
#define NIL -1
using namespace std;

// A class that represents an undirected graph
class Graph
{
    int V; // No. of vertices
    list<int> *adj; // A dynamic array of adjacency lists
    void bridgeUtil(int src,vector<bool>&vis,vector<int>&disc,vector<int>&low,int& time,int parent);
public:
    Graph(int V); // Constructor
    void addEdge(int v, int w); // to add an edge to graph
    void bridge(); // prints all bridges
};

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

void Graph::addEdge(int v, int w)
{
    adj[v].push_back(w);
    adj[w].push_back(v); // Note: the graph is undirected
}

// A recursive function that finds and prints bridges using
// DFS traversal
// u --> The vertex to be visited next
// visited[] --> keeps tract of visited vertices
// disc[] --> Stores discovery times of visited vertices
// parent[] --> Stores parent vertices in DFS tree
void Graph::bridgeUtil(int src,vector<bool>&vis,vector<int>&disc,vector<int>&low,int& time,int parent)
{
    vis[src]=true;
    disc[src]=time;
    low[src]=time;
    time++;
    for(auto it=adj[src].begin();it!=adj[src].end();it++){
        if(!vis[*it]){
            bridgeUtil(*it,vis,disc,low,time,src);
            low[src]=min(low[src],low[*it]);
            if(low[*it]>disc[src]){
                cout<<src<<" "<<*it<<endl;
            }


        }
        else if(parent!=*it){
            low[src]=min(low[src],disc[*it]);

        }

    }
}


void Graph::bridge()
{
    vector<bool>vis(V,false);
    vector<int>disc(V,-1);
    vector<int>low(V,-1);
    vector<int>parent();
    int time=0;
    for(int i=0;i<V;i++){
        if(!vis[i]){
            bridgeUtil(i,vis,disc,low,time,-1);

        }

    }

}

// Driver program to test above function
int main()
{
    // Create graphs given in above diagrams
    cout << "\nBridges in first graph \n";
    Graph g1(5);
    g1.addEdge(1, 0);
    g1.addEdge(0, 2);
    g1.addEdge(2, 1);
    g1.addEdge(0, 3);
    g1.addEdge(3, 4);
    g1.bridge();

    cout << "\nBridges in second graph \n";
    Graph g2(4);
    g2.addEdge(0, 1);
    g2.addEdge(1, 2);
    g2.addEdge(2, 3);
    g2.bridge();

    cout << "\nBridges in third graph \n";
    Graph g3(7);
    g3.addEdge(0, 1);
    g3.addEdge(1, 2);
    g3.addEdge(2, 0);
    g3.addEdge(1, 3);
    g3.addEdge(1, 4);
    g3.addEdge(1, 6);
    g3.addEdge(3, 5);
    g3.addEdge(4, 5);
    g3.bridge();

    return 0;
}