Add BFS implementation

Author: jcazevedo

src/main/java/com/packt/datastructuresandalg/lesson6/bfs/Graph.java

@@ -0,0 +1,73 @@
+package com.packt.datastructuresandalg.lesson6.bfs;
+
+import java.util.ArrayList;
+import java.util.LinkedList;
+import java.util.Queue;
+
+public class Graph {
+    ArrayList<Integer> adj[];
+
+    public Graph(int nodes) {
+        this.adj = new ArrayList[nodes];
+        for (int i = 0; i < nodes; i++) {
+            this.adj[i] = new ArrayList<>();
+        }
+    }
+
+    public void addEdge(int u, int v) {
+        this.adj[u].add(v);
+    }
+
+    public int[] bfs(int start) {
+        int[] parent = new int[this.adj.length];
+        boolean[] visited = new boolean[this.adj.length];
+
+        for (int i = 0; i < this.adj.length; i++) {
+            parent[i] = -1;
+            visited[i] = false;
+        }
+
+        visited[start] = true;
+        Queue<Integer> q = new LinkedList<>();
+        q.add(start);
+        while (!q.isEmpty()) {
+            int current = q.remove();
+            for (int i = 0; i < this.adj[current].size(); i++) {
+                int next = this.adj[current].get(i);
+                if (!visited[next]) {
+                    visited[next] = true;
+                    parent[next] = current;
+                    q.add(next);
+                }
+            }
+        }
+        return parent;
+    }
+
+    public static void main(String [] args) {
+        Graph g = new Graph(6);
+        g.addEdge(0, 1);
+        g.addEdge(0, 3);
+        g.addEdge(1, 4);
+        g.addEdge(2, 4);
+        g.addEdge(2, 5);
+        g.addEdge(3, 1);
+        g.addEdge(4, 3);
+        g.addEdge(5, 5);
+        int[] parent = g.bfs(2);
+        for (int i = 0; i < 6; i++) {
+            System.out.print("Path from 2 to " + i + ":");
+            if (parent[i] == -1 && i != 2)
+                System.out.println(" None");
+            else {
+                String path = "";
+                int j = i;
+                while (j != -1) {
+                    path = (" " + j) + path;
+                    j = parent[j];
+                }
+                System.out.println(path);
+            }
+        }
+    }
+}