Java Program to Perform Preorder Non-Recursive Traversal of a Given Binary Tree

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This is a java program to construct a binary tree and perform preorder traversal of the constructed binary tree.
Nodes visited are in the order:
visit Root node
visit Left node
visit Right node

Here is the source code of the Java Program to Perform Preorder Non-Recursive Traversal of a Given Binary Tree. The Java program is successfully compiled and run on a Windows system. The program output is also shown below.

  1. //This is a java program to implement non recursive pre-order traversal of Binary Search Tree
  2. import java.util.Scanner;
  3. import java.util.Stack;
  4.  
  5. class BinarySearchTreeNode
  6. {
  7.     BinarySearchTreeNode left, right;
  8.     int                  data;
  9.  
  10.     public BinarySearchTreeNode()
  11.     {
  12.         left = null;
  13.         right = null;
  14.         data = 0;
  15.     }
  16.  
  17.     public BinarySearchTreeNode(int n)
  18.     {
  19.         left = null;
  20.         right = null;
  21.         data = n;
  22.     }
  23.  
  24.     public void setLeft(BinarySearchTreeNode n)
  25.     {
  26.         left = n;
  27.     }
  28.  
  29.     public void setRight(BinarySearchTreeNode n)
  30.     {
  31.         right = n;
  32.     }
  33.  
  34.     public BinarySearchTreeNode getLeft()
  35.     {
  36.         return left;
  37.     }
  38.  
  39.     public BinarySearchTreeNode getRight()
  40.     {
  41.         return right;
  42.     }
  43.  
  44.     public void setData(int d)
  45.     {
  46.         data = d;
  47.     }
  48.  
  49.     public int getData()
  50.     {
  51.         return data;
  52.     }
  53. }
  54.  
  55. class BinarySearchTreeOperations
  56. {
  57.     private BinarySearchTreeNodes root;
  58.  
  59.     public BinarySearchTreeOperations()
  60.     {
  61.         root = null;
  62.     }
  63.  
  64.     public boolean isEmpty()
  65.     {
  66.         return root == null;
  67.     }
  68.  
  69.     public void insert(int data)
  70.     {
  71.         root = insert(root, data);
  72.     }
  73.  
  74.     private BinarySearchTreeNodes insert(BinarySearchTreeNodes node, int data)
  75.     {
  76.         if (node == null)
  77.             node = new BinarySearchTreeNodes(data);
  78.         else
  79.         {
  80.             if (data <= node.getData())
  81.                 node.left = insert(node.left, data);
  82.             else
  83.                 node.right = insert(node.right, data);
  84.         }
  85.         return node;
  86.     }
  87.  
  88.     public void preorder()
  89.     {
  90.         preorder(root);
  91.     }
  92.  
  93.     private void preorder(BinarySearchTreeNodes r)
  94.     {
  95.         Stack<BinarySearchTreeNodes> s = new Stack<BinarySearchTreeNodes>();
  96.         s.push(r);
  97.         while (!s.empty())
  98.         {
  99.             r = s.pop();
  100.             System.out.print(r.data + " ");
  101.             if (r.right != null)
  102.                 s.push(r.right);
  103.             if (r.left != null)
  104.                 s.push(r.left);
  105.         }
  106.     }
  107. }
  108.  
  109. public class Preorder_NonRecursive_BST
  110. {
  111.     public static void main(String[] args)
  112.     {
  113.         Scanner scan = new Scanner(System.in);
  114.         BinarySearchTreeOperations bst = new BinarySearchTreeOperations();
  115.         System.out.println("Enter the first 10 elements of the tree\n");
  116.         int N = 10;
  117.         for (int i = 0; i < N; i++)
  118.             bst.insert(scan.nextInt());
  119.  
  120.         System.out.print("\nPre order  : ");
  121.         bst.preorder();
  122.  
  123.         scan.close();
  124.     }
  125. }

Output:

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$ javac Preorder_NonRecursive_BST.java
$ java Preorder_NonRecursive_BST
 
Enter the first 10 elements of the tree
 
12 4 10 13 15 46 78 98 45 12
 
Pre order  : 12 4 10 12 13 15 46 45 78 98

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer & SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage, Advanced C Programming, SAN Storage Technologies, SCSI Internals & Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him @ LinkedIn