solution.cpp

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

#define NIL -1

//GeeksforGeeks

class Graph {
    int V;
    list < int > * adj;
    void bridgeUtil(int v, bool visited[], int disc[], int low[],
        int parent[]);
    public:
        Graph(int V);
    void addEdge(int v, int w);
    void bridge();
};

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);
}

void Graph::bridgeUtil(int u, bool visited[], int disc[], int low[], int parent[]) {
    static int time = 0;
    visited[u] = true;
    disc[u] = low[u] = ++time;
    list < int > ::iterator i;
    for (i = adj[u].begin(); i != adj[u].end(); ++i) {
        int v = * i;
        if (!visited[v]) {
            parent[v] = u;
            bridgeUtil(v, visited, disc, low, parent);
            low[u] = min(low[u], low[v]);
            if (low[v] > disc[u])
                cout << u << " " << v << endl;
        } else if (v != parent[u])
            low[u] = min(low[u], disc[v]);
    }
}

void Graph::bridge() {
    bool * visited = new bool[V];
    int * disc = new int[V];
    int * low = new int[V];
    int * parent = new int[V];
    for (int i = 0; i < V; i++) {
        parent[i] = NIL;
        visited[i] = false;
    }
    for (int i = 0; i < V; i++)
        if (visited[i] == false)
            bridgeUtil(i, visited, disc, low, parent);
}

int main() {
  freopen("input.txt", "r", stdin);
  freopen("output.txt", "w", stdout);
  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;
}