C++ Programming Code Examples C++ > Computer Graphics Code Examples Program to Find the Shortest Path Between Two Vertices Using Dijkstra's Algorithm Program to Find the Shortest Path Between Two Vertices Using Dijkstra's Algorithm This is a C++ Program to check whether path exists between two given nodes. The idea is to run the depth first search algorithm with the given source node, if during dfs we visit destination node, path exists, not otherwise. #include <iostream> #include <list> using namespace std; // This class represents a directed graph using adjacency list representation class Graph { int V; // No. of vertices list<int> *adj; // Pointer to an array containing adjacency lists public: Graph(int V); // Constructor void addEdge(int v, int w); // function to add an edge to graph bool isReachable(int s, int d); // returns true if there is a path from s to d }; 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 v's list. } // A BFS based function to check whether d is reachable from s. bool Graph::isReachable(int s, int d) { // Base case if (s == d) return true; // Mark all the vertices as not visited bool *visited = new bool[V]; for (int i = 0; i < V; i++) visited[i] = false; // Create a queue for BFS list<int> queue; // Mark the current node as visited and enqueue it visited[s] = true; queue.push_back(s); // it will be used to get all adjacent vertices of a vertex list<int>::iterator i; while (!queue.empty()) { // Dequeue a vertex from queue and print it s = queue.front(); queue.pop_front(); // Get all adjacent vertices of the dequeued vertex s // If a adjacent has not been visited, then mark it visited // and enqueue it for (i = adj[s].begin(); i != adj[s].end(); ++i) { // If this adjacent node is the destination node, then return true if (*i == d) return true; // Else, continue to do BFS if (!visited[*i]) { visited[*i] = true; queue.push_back(*i); } } } return false; } // Driver program to test methods of graph class int main() { // Create a graph given in the above diagram Graph g(4); g.addEdge(0, 1); g.addEdge(0, 2); g.addEdge(1, 2); g.addEdge(2, 0); g.addEdge(2, 3); g.addEdge(3, 3); cout << "Enter the source and destination vertices: (0-3)"; int u, v; cin >> u >> v; if (g.isReachable(u, v)) cout << "\nThere is a path from " << u << " to " << v; else cout << "\nThere is no path from " << u << " to " << v; int temp; temp = u; u = v; v = temp; if (g.isReachable(u, v)) cout << "\nThere is a path from " << u << " to " << v; else cout << "\nThere is no path from " << u << " to " << v; return 0; }