Create bfs_traversal.cpp

bfs_traversal.cpp

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+// C++ code to print BFS traversal from a given
+// source vertex
+
+#include <bits/stdc++.h>
+using namespace std;
+
+// This class represents a directed graph using
+// adjacency list representation
+class Graph {
+
+	// No. of vertices
+	int V;
+
+	// Pointer to an array containing adjacency lists
+	vector<list<int> > adj;
+
+public:
+	// Constructor
+	Graph(int V);
+
+	// Function to add an edge to graph
+	void addEdge(int v, int w);
+
+	// Prints BFS traversal from a given source s
+	void BFS(int s);
+};
+
+Graph::Graph(int V)
+{
+	this->V = V;
+	adj.resize(V);
+}
+
+void Graph::addEdge(int v, int w)
+{
+	// Add w to v’s list.
+	adj[v].push_back(w);
+}
+
+void Graph::BFS(int s)
+{
+	// Mark all the vertices as not visited
+	vector<bool> visited;
+	visited.resize(V, 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);
+
+	while (!queue.empty()) {
+
+		// Dequeue a vertex from queue and print it
+		s = queue.front();
+		cout << s << " ";
+		queue.pop_front();
+
+		// Get all adjacent vertices of the dequeued
+		// vertex s.
+		// If an adjacent has not been visited,
+		// then mark it visited and enqueue it
+		for (auto adjacent : adj[s]) {
+			if (!visited[adjacent]) {
+				visited[adjacent] = true;
+				queue.push_back(adjacent);
+			}
+		}
+	}
+}
+
+// Driver code
+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 << "Following is Breadth First Traversal "
+		<< "(starting from vertex 2) \n";
+	g.BFS(2);
+
+	return 0;
+}