Binary Search Tree Traversal

Author: shashankvishwakarma

src/main/java/dsa/trees/BinarySearchTreeTraversal.java

@@ -1,5 +1,7 @@
 package dsa.trees;
 
+import java.util.LinkedList;
+import java.util.Queue;
 import java.util.Scanner;
 
 public class BinarySearchTreeTraversal extends BinaryTree {
@@ -43,9 +45,57 @@ private void postOrder(Node node) {
         System.out.print(node.getRight() + " ");
     }
 
+    public static void levelOrder(Node node) {
+        if (node == null) {
+            return;
+        }
+        Queue<Node> q = new LinkedList<>();
+        q.add(node);
+        q.add(null);
+        while (!q.isEmpty()) {
+            Node curr = q.remove();
+            if (curr == null) {
+                System.out.println();
+                //queue empty
+                if (q.isEmpty()) {
+                    break;
+                } else {
+                    q.add(null);
+                }
+            } else {
+                System.out.print(curr.getValue() + " ");
+                if (curr.getLeft() != null) {
+                    q.add(curr.getLeft());
+                }
+                if (curr.getRight() != null) {
+                    q.add(curr.getRight());
+                }
+            }
+        }
+    }
+
+
     public static void main(String[] args) {
-        Scanner scanner = new Scanner(System.in);
         BinarySearchTreeTraversal binarySearchTreeTraversal = new BinarySearchTreeTraversal();
+
+        //buildTreeAndTraversalApproach1(binarySearchTreeTraversal);
+
+        buildTreeAndTraversalApproach2(binarySearchTreeTraversal);
+
+    }
+
+    private static void buildTreeAndTraversalApproach2(BinarySearchTreeTraversal binarySearchTreeTraversal) {
+        int[] nodes = {1, 2, 4, -1, -1, 5, -1, -1, 3, -1, 6, -1, -1};
+
+        Node root = binarySearchTreeTraversal.buildPreOrderTree(nodes);
+        System.out.println(root.getValue());
+        binarySearchTreeTraversal.display(root);
+        levelOrder(root);
+    }
+
+    private static void buildTreeAndTraversalApproach1(BinarySearchTreeTraversal binarySearchTreeTraversal) {
+        Scanner scanner = new Scanner(System.in);
+
         binarySearchTreeTraversal.populate(scanner);
         System.out.println("Tree values in structured format:");
         binarySearchTreeTraversal.display();

src/main/java/dsa/trees/BinaryTree.java

@@ -5,6 +5,7 @@
 public class BinaryTree {
 
     private Node root;
+    static private int idx = -1;
 
     public static class Node {
         private int value;
@@ -77,6 +78,21 @@ private void populate(Scanner scanner, Node node) {
         }
     }
 
+    public Node buildPreOrderTree(int[] nodes) {
+        idx++;
+        if (nodes[idx] == -1) {
+            return null;
+        }
+        Node newNode = new Node(nodes[idx]);
+        newNode.left = buildPreOrderTree(nodes);
+        newNode.right = buildPreOrderTree(nodes);
+        return newNode;
+    }
+
+    public void display(Node root) {
+        display(root, "Root Node: ");
+    }
+
     public void display() {
         display(this.root, "Root Node: ");
     }