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C++ Program to Find Strongly Connected Components in Graphs
Weakly or Strongly Connected for a given a directed graph can be found out using DFS. This is a C++ program of this problem.
Functions used
Begin Function fillorder() = fill stack with all the vertices. a) Mark the current node as visited and print it b) Recur for all the vertices adjacent to this vertex c) All vertices reachable from v are processed by now, push v to Stack End Begin Function DFS() : a) Mark the current node as visited and print it b) Recur for all the vertices adjacent to this vertex End
Example
#include <iostream> #include <list> #include <stack> using namespace std; class G { int m; list<int> *adj; //declaration of functions void fillOrder(int n, bool visited[], stack<int> &Stack); void DFS(int n, bool visited[]); public: G(int N); //constructor void addEd(int v, int w); int print(); G getTranspose(); }; G::G(int m) { this->m = m; adj = new list<int> [m]; } void G::DFS(int n, bool visited[]) { visited[n] = true; // Mark the current node as visited and print it cout << n << " "; list<int>::iterator i; //Recur for all the vertices adjacent to this vertex for (i = adj[n].begin(); i != adj[n].end(); ++i) if (!visited[*i]) DFS(*i, visited); } G G::getTranspose() { G g(m); for (int n = 0; n< m; n++) { list<int>::iterator i; for (i = adj[n].begin(); i != adj[n].end(); ++i) { g.adj[*i].push_back(n); } } return g; } void G::addEd(int v, int w) { adj[v].push_back(w); //add w to v's list } void G::fillOrder(int v, bool visited[], stack<int> &Stack) { visited[v] = true; //Mark the current node as visited and print it list<int>::iterator i; //Recur for all the vertices adjacent to this vertex for (i = adj[v].begin(); i != adj[v].end(); ++i) if (!visited[*i]) fillOrder(*i, visited, Stack); Stack.push(v); } int G::print() { //print the solution stack<int> Stack; bool *visited = new bool[m]; for (int i = 0; i < m; i++) visited[i] = false; for (int i = 0; i < m; i++) if (visited[i] == false) fillOrder(i, visited, Stack); G graph= getTranspose(); //Create a reversed graph for (int i = 0; i < m; i++)//Mark all the vertices as not visited visited[i] = false; int count = 0; //now process all vertices in order defined by Stack while (Stack.empty() == false) { int v = Stack.top(); Stack.pop(); //pop vertex from stack if (visited[v] == false) { graph.DFS(v, visited); cout << endl; } count++; } return count; } int main() { G g(5); g.addEd(2, 1); g.addEd(3, 2); g.addEd(1, 0); g.addEd(0, 3); g.addEd(3, 1); cout << "Following are strongly connected components in given graph \n"; if (g.print() > 1) { cout << "Graph is weakly connected."; } else { cout << "Graph is strongly connected."; } return 0; }
Output
Following are strongly connected components in given graph 4 0 1 2 3 Graph is weakly connected.
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