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This is 5th part of java binary tree tutorial.
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
In this post, we will see about Level Order binary tree traversal in java.
Level Order traversal:
Level order traversal of below tree will be:
We will use Queue for Level Order traversal.This algorithm is very similar to Breadth first search of graph.
Steps for Level order traversal algorithm:
- Create empty queue and pust root node to it.
- Do the following when queue is not empty
- Pop a node from queue and print it
- Push left child of popped node to queue if not null
- Push right child of popped node to queue if not null
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// prints in level order public static void levelOrderTraversal(TreeNode startNode) { Queue<TreeNode> queue=new LinkedList<TreeNode>(); queue.add(startNode); while(!queue.isEmpty()) { TreeNode tempNode=queue.poll(); System.out.printf("%d ",tempNode.data); if(tempNode.left!=null) queue.add(tempNode.left); if(tempNode.right!=null) queue.add(tempNode.right); } } |
Example:
Lets say your binary tree is :
So Level Order traversal will work as below:
Lets create java program for level order traversal:
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package org.arpit.java2blog.binarytree; import java.util.Queue; import java.util.LinkedList; public class BinaryTreeLevelOrder { public static class TreeNode { int data; TreeNode left; TreeNode right; TreeNode(int data) { this.data=data; } } // prints in level order public static void levelOrderTraversal(TreeNode startNode) { Queue<TreeNode> queue=new LinkedList<TreeNode>(); queue.add(startNode); while(!queue.isEmpty()) { TreeNode tempNode=queue.poll(); System.out.printf("%d ",tempNode.data); if(tempNode.left!=null) queue.add(tempNode.left); if(tempNode.right!=null) queue.add(tempNode.right); } } public static void main(String[] args) { // Creating a binary tree TreeNode rootNode=createBinaryTree(); System.out.println("Level Order traversal of binary tree will be:"); levelOrderTraversal(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:
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Level Order traversal of binary tree will be: 40 20 60 10 30 50 70 |
Please go through java interview programs for more such programs.
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You have a typo after explain how Level Order traversal works on “Lets create java program for PreOrder traversal:” it is not PreOrder, anyway everything is well explained and is easy to see that is a typo.
Really good explanation
Good