get level of a node in binary tree in java

If you want to practice data structure and algorithm programs, you can go through data structure and algorithm interview questions.
This is 11th 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 Print leaf nodes of binary tree Count leaf nodes in binary tree Print all paths from root to leaf in binary tree Print vertical sum of binary tree in java

In this post, we will see about program to get level of node  in a binary tree in java.
We will search for a key in binary tree. Root will be at level 1. If we do not find key in binary tree then its level will be 0. 

Algorithm :

Steps for getting level of a node in binary tree:
  • If node is null then return 0
  • If node's data is equal to key, then return level.
  • Recursively search key in left subtree 
  • If not found, then search in right subtree

Code for recursion will be:

/* To get level of node in a binary tree*/
  public static int getLevelOfNode(TreeNode root,int key,int level)
 {
  if(root==null)
   return 0;
  if(root.data==key)
   return level;
  
  int result=getLevelOfNode(root.left,key,level+1) ;
  if(result!=0)
  { 
   // If found in left subtree , return 
   return result;
  
  }
  result= getLevelOfNode(root.right,key,level+1);
 
  return result;
 }

Lets create java program to get level of node in binary tree:

Lets say, your binary tree is this:
package org.arpit.java2blog;

public class BinaryTree {

 
 public static class TreeNode
 {
  int data;
  TreeNode left;
  TreeNode right;
  TreeNode(int data)
  {
   this.data=data;
  }
 }
 
 // Recursive Solution
//To get level of node in a binary tree
 public static int getLevelOfNode(TreeNode root,int key,int level)
 {
  if(root==null)
   return 0;
  if(root.data==key)
   return level;
  
  int result=getLevelOfNode(root.left,key,level+1) ;
  if(result!=0)
  { 
   // If found in left subtree , return 
   return result;
  }
  result= getLevelOfNode(root.right,key,level+1);
 
  return result;
 }

 
 public static void main(String[] args)
 {
  BinaryTree bi=new BinaryTree();
  // Creating a binary tree
  TreeNode rootNode=createBinaryTree();
  System.out.println("Node data: 70,Level :"+getLevelOfNode(rootNode, 70, 1));
  System.out.println("Node data: 100,Level :"+getLevelOfNode(rootNode, 100, 1));
  System.out.println("Node data: 60,Level :"+getLevelOfNode(rootNode, 60, 1));
  System.out.println("Node data: 40,Level :"+getLevelOfNode(rootNode, 40, 1));
 }
 
 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:
 
Node data: 70,Level :3
Node data: 100,Level :0
Node data: 60,Level :2
Node data: 40,Level :1

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 Interview programs in java  for more such programs.

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