Update Breadth-First Search (BFS) Searching .java

Java/Algorithm/SearchingAlgorithm/Breadth-First Search (BFS) Searching .java

@@ -1,40 +1,44 @@
 import java.util.*;
 
-public class BFS {
+public class Graph {
     private int V; // Number of vertices
-    private LinkedList<Integer> adj[]; // Adjacency list representation of the graph
+    private LinkedList<Integer> adj[]; // Adjacency List
 
-    public BFS(int v) {
+    // Constructor
+    Graph(int v) {
         V = v;
         adj = new LinkedList[v];
         for (int i = 0; i < v; ++i)
             adj[i] = new LinkedList();
     }
 
-    // Function to add an edge into the graph
+    // Add an edge to the graph
     void addEdge(int v, int w) {
-        adj[v].add(w);
+        if (v >= 0 && v < V && w >= 0 && w < V) {
+            adj[v].add(w);
+        } else {
+            throw new IllegalArgumentException("Invalid edge: " + v + " -> " + w);
+        }
     }
 
-    // BFS traversal starting from a given source vertex
+    // BFS traversal from a given source s
     void BFS(int s) {
         // Mark all the vertices as not visited
         boolean visited[] = new boolean[V];
 
         // Create a queue for BFS
-        LinkedList<Integer> queue = new LinkedList<>();
+        LinkedList<Integer> queue = new LinkedList<Integer>();
 
         // Mark the current node as visited and enqueue it
         visited[s] = true;
         queue.add(s);
 
         while (queue.size() != 0) {
-            // Dequeue a vertex from the queue and print it
+            // Dequeue a vertex from queue and print it
             s = queue.poll();
             System.out.print(s + " ");
 
-            // Get all adjacent vertices of the dequeued vertex s. If an adjacent vertex has not been visited,
-            // then mark it visited and enqueue it
+            // Get all adjacent vertices of the dequeued vertex s.
             Iterator<Integer> i = adj[s].listIterator();
             while (i.hasNext()) {
                 int n = i.next();
@@ -46,26 +50,46 @@ void BFS(int s) {
         }
     }
 
+    // Driver method to
     public static void main(String args[]) {
         Scanner scanner = new Scanner(System.in);
 
-        System.out.print("Enter the number of vertices: ");
-        int V = scanner.nextInt();
+        try {
+            System.out.print("Enter the number of vertices: ");
+            int V = scanner.nextInt();
+            if (V <= 0) {
+                throw new IllegalArgumentException("Number of vertices must be positive.");
+            }
 
-        BFS graph = new BFS(V);
+            Graph g = new Graph(V);
 
-        System.out.println("Enter the edges (vertex pairs, -1 to stop): ");
-        while (true) {
-            int v1 = scanner.nextInt();
-            if (v1 == -1) break;
-            int v2 = scanner.nextInt();
-            graph.addEdge(v1, v2);
-        }
+            System.out.println("Enter the number of edges: ");
+            int E = scanner.nextInt();
+            if (E < 0) {
+                throw new IllegalArgumentException("Number of edges must be non-negative.");
+            }
 
-        System.out.print("Enter the starting vertex for BFS: ");
-        int startVertex = scanner.nextInt();
+            System.out.println("Enter the edges (source destination): ");
+            for (int i = 0; i < E; i++) {
+                int source = scanner.nextInt();
+                int destination = scanner.nextInt();
+                g.addEdge(source, destination);
+            }
+
+            System.out.print("Enter the starting vertex for BFS: ");
+            int startVertex = scanner.nextInt();
+            if (startVertex < 0 || startVertex >= V) {
+                throw new IllegalArgumentException("Starting vertex is out of bounds.");
+            }
 
-        System.out.println("Breadth First Traversal starting from vertex " + startVertex + ":");
-        graph.BFS(startVertex);
+            System.out.println("BFS Traversal starting from vertex " + startVertex + ":");
+            g.BFS(startVertex);
+        } catch (InputMismatchException e) {
+            System.out.println("Invalid input. Please enter integers only.");
+        } catch (IllegalArgumentException e) {
+            System.out.println(e.getMessage());
+        } finally {
+            scanner.close();
+        }
     }
 }