C++ Programming Code Examples C++ > Computer Graphics Code Examples Check Whether it is Weakly Connected or Strongly Connected for a Directed Graph Check Whether it is Weakly Connected or Strongly Connected for a Directed Graph This is a C++ Program to find the connected components of the undirected graph. This can be done using depth first search algorithm. #include <iostream> #include <list> #include <stack> using namespace std; class Graph { int V; // No. of vertices list<int> *adj; // An array of adjacency lists // Fills Stack with vertices (in increasing order of finishing times) // The top element of stack has the maximum finishing time void fillOrder(int v, bool visited[], stack<int> &Stack); // A recursive function to print DFS starting from v void DFSUtil(int v, bool visited[]); public: Graph(int V); void addEdge(int v, int w); // The main function that finds and prints strongly connected components int printSCCs(); // Function that returns reverse (or transpose) of this graph Graph getTranspose(); }; Graph::Graph(int V) { this->V = V; adj = new list<int> [V]; } // A recursive function to print DFS starting from v void Graph::DFSUtil(int v, bool visited[]) { // Mark the current node as visited and print it visited[v] = true; cout << v << " "; // 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]) DFSUtil(*i, visited); } Graph Graph::getTranspose() { Graph g(V); for (int v = 0; v < V; v++) { // Recur for all the vertices adjacent to this vertex list<int>::iterator i; for (i = adj[v].begin(); i != adj[v].end(); ++i) { g.adj[*i].push_back(v); } } return g; } void Graph::addEdge(int v, int w) { adj[v].push_back(w); // Add w to v's list. } void Graph::fillOrder(int v, bool visited[], stack<int> &Stack) { // Mark the current node as visited and print it visited[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]) fillOrder(*i, visited, Stack); // All vertices reachable from v are processed by now, push v to Stack Stack.push(v); } // The main function that finds and prints all strongly connected components int Graph::printSCCs() { stack<int> Stack; // Mark all the vertices as not visited (For first DFS) bool *visited = new bool[V]; for (int i = 0; i < V; i++) visited[i] = false; // Fill vertices in stack according to their finishing times for (int i = 0; i < V; i++) if (visited[i] == false) fillOrder(i, visited, Stack); // Create a reversed graph Graph gr = getTranspose(); // Mark all the vertices as not visited (For second DFS) for (int i = 0; i < V; i++) visited[i] = false; int count = 0; // Now process all vertices in order defined by Stack while (Stack.empty() == false) { // Pop a vertex from stack int v = Stack.top(); Stack.pop(); // Print Strongly connected component of the popped vertex if (visited[v] == false) { gr.DFSUtil(v, visited); cout << endl; } count++; } return count; } // Driver program to test above functions int main() { // Create a graph given in the above diagram Graph g(5); g.addEdge(1, 0); g.addEdge(0, 2); g.addEdge(2, 1); g.addEdge(0, 3); g.addEdge(3, 4); cout << "Following are strongly connected components in given graph \n"; if (g.printSCCs() > 1) { cout << "Graph is weakly connected."; } else { cout << "Graph is strongly connected."; } return 0; }