Binary Tree InOrder traversal in java

If you want to practice data structure and algorithm programs, you can go through data structure and algorithm interview questions.
This is 4th part of java binary tree tutorial.
In this post, we will see about InOrder binary tree traversal in java.

InOrder traversal:

In InOrder traversal,each node is processed between subtrees.In simpler words,Visit left subtree, node and then right subtree.
Steps for InOrder traversal are:
  • Traverse the left subtree in InOrder.
  • Visit the node.
  • Traverse the right subtree in InOrder.
 There can be two ways of implementing it
  • Recursive
  • Iterative
Recursive solution:
Recursive solution is very straight forward.Below diagram will make you understand recursion better.

Code for recursion will be:
public void inOrder(TreeNode root) {
  if(root !=  null) {
   inOrder(root.left);
   //Visit the node by Printing the node data  
   System.out.printf("%d ",root.data);
   inOrder(root.right);
  }
 }
Iterative solution:
For recursion, we use implicit stack. So here to convert recursive solution to iterative, we will use explicit stack.
Steps for iterative solution:
  1. Create an empty stack s and Initialize current node as root
  2. Push the current node to s and set currentNode = currentNode.left until currentNode is NULL
  3. If currentNode is NULL and s is not empty then
    • Pop the top node from stack and print it
    •  set currentNode = currentNode.right
    • go to step 2
  4. If stack is empty and currentNode is also null then we are done with it
 
public void inOrderIter(TreeNode root) {

  if(root == null)
   return;

  Stack<TreeNode> s = new Stack<TreeNode>();
  TreeNode currentNode=root;

  while(!s.empty() || currentNode!=null){

   if(currentNode!=null)
   {
    s.push(currentNode);
    currentNode=currentNode.left;
   }
   else
   {
    TreeNode n=s.pop();
    System.out.printf("%d ",n.data);
    currentNode=n.right;
   }
  }
 }

Lets create java program for InOrder traversal:
 
package org.arpit.java2blog;

import java.util.Stack;

public class BinaryTree {

 
 public static class TreeNode
 {
  int data;
  TreeNode left;
  TreeNode right;
  TreeNode(int data)
  {
   this.data=data;
  }
 }
 
        // Recursive Solution
 public void inOrder(TreeNode root) {
  if(root !=  null) {
   inOrder(root.left);
   //Visit the node by Printing the node data  
   System.out.printf("%d ",root.data);
   inOrder(root.right);
  }
 }
 
  // Iterative solution
 public void inOrderIter(TreeNode root) {

  if(root == null)
   return;

  Stack<TreeNode> s = new Stack<TreeNode>();
  TreeNode currentNode=root;

  while(!s.empty() || currentNode!=null){

   if(currentNode!=null)
   {
    s.push(currentNode);
    currentNode=currentNode.left;
   }
   else
   {
    TreeNode n=s.pop();
    System.out.printf("%d ",n.data);
    currentNode=n.right;
   }
  }
 }
 
 public static void main(String[] args)
 {
  BinaryTree bi=new BinaryTree();
  // Creating a binary tree
  TreeNode rootNode=createBinaryTree();
  System.out.println("Using Recursive solution:");

  bi.inOrder(rootNode);

  System.out.println();
  System.out.println("-------------------------");
  System.out.println("Using Iterative solution:");

  bi.inOrderIter(rootNode);
 }
 
 public static TreeNode createBinaryTree()
 {
  
  TreeNode rootNode =new TreeNode(40);
  TreeNode node20=new TreeNode(20);
  TreeNode node10=new TreeNode(10);
  TreeNode node30=new TreeNode(30);
  TreeNode node60=new TreeNode(60);
  TreeNode node50=new TreeNode(50);
  TreeNode node70=new TreeNode(70);
  
  rootNode.left=node20;
  rootNode.right=node60;
  
  node20.left=node10;
  node20.right=node30;
  
  node60.left=node50;
  node60.right=node70;
  
  return rootNode;
 }
}
Run above program and you will get following output:
 
Using Recursive solution:
10 20 30 40 50 60 70 
-------------------------
Using Iterative solution:
10 20 30 40 50 60 70  

Java Binary tree tutorial:

    Binary tree in java Binary tree preorder traversal Binary tree postorder traversal Binary tree inorder traversal Binary tree level order traversal Binary tree spiral order traversal Binary tree reverse level order traversal Binary tree boundary traversal Print leaf nodes of binary tree Count leaf nodes in binary tree get maximum element in binary tree Print all paths from root to leaf in binary tree Print vertical sum of binary tree in java Get level of node in binary tree in java Lowest common ancestor(LCA) in binary tree in java

Please go through java interview programs for more such programs.

Written by Arpit:

If you have read the post and liked it. Please connect with me on Facebook | Twitter | Google Plus

 

Java tutorial for beginners Copyright © 2012