Algorithms

Print nodes at k distance from the root

In this article, we will discuss how to print nodes at k distance from the root of a binary tree. The trees are hierarchical data structures unlike Arrays, Linked Lists, Stack and queues, which are linear data structures. In the tree, the topmost node is known as the root of the tree. Other elements that are directly under an element are called its children. The element directly above something is called its parent. Let’s see the following diagram of the binary tree data structure:

 tree
      ----
       j    <-- root
     /   \
    f      k  
  /   \      \
 a     h      z    <-- leaves

Let’s see the tree node representation in Java code like the following:

/**
 * Class containing left and right child of current node and key value
 */
package com.dineshonjava.algo;

/**
 * @author Dinesh.Rajput
 *
 */
public class TreeNode {
	
	int data;
	TreeNode left, right;
    TreeNode(int item)
    {
        data = item;
        left = right = null;
    }
}

In previous articles we have discussed some important algorithm related to the linked list like the following:

Let’s discuss the algorithm to print nodes at k distance from the root of the binary tree.

Print nodes at k distance from the root

Given a root of a tree, and an integer k. Print all the nodes which are at k distance from the root. Let’s see the following code:

/**
 * 
 */
package com.dineshonjava.algo;

/**
 * @author Dinesh.Rajput
 *
 */
public class TreeTest {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		TreeNode root = new TreeNode(0); 
        
        root.left = new TreeNode(1); 
        root.right = new TreeNode(2); 
        
        root.left.left = new TreeNode(3); 
        root.left.right = new TreeNode(4); 
        root.right.left = new TreeNode(5); 
        root.right.right = new TreeNode(6);
        
        root.left.left.left = new TreeNode(7); 
        root.left.left.right = new TreeNode(8); 
        root.left.right.left = new TreeNode(9); 
        root.left.right.right = new TreeNode(10);
        
        root.right.left.left = new TreeNode(11); 
        root.right.left.right = new TreeNode(12); 
        root.right.right.left = new TreeNode(13); 
        root.right.right.right = new TreeNode(14);
        
        System.out.println("Nodes at 3 distance from the root");
        printKDistant(root, 3); 
	}

	private static void printKDistant(TreeNode node, int k) {
		if (node == null) 
            return; 
        if (k == 0)  
        { 	
            System.out.print(node.data + " "); 
            return; 
        }  
        else 
        { 
            printKDistant(node.left, k - 1); 
            printKDistant(node.right, k - 1); 
        } 
	}

}

Run above program, you will get the following output:

Nodes at 3 distance from the root
7 8 9 10 11 12 13 14 

As you can see the above output, we have printed all nodes with distance 3.

Hope, you have understood this solution for the above to print nodes at k distance from the root. Please share other solutions if you have. :).

Happy learning with us!!!.

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Dinesh Rajput

Dinesh Rajput is the chief editor of a website Dineshonjava, a technical blog dedicated to the Spring and Java technologies. It has a series of articles related to Java technologies. Dinesh has been a Spring enthusiast since 2008 and is a Pivotal Certified Spring Professional, an author of a book Spring 5 Design Pattern, and a blogger. He has more than 10 years of experience with different aspects of Spring and Java design and development. His core expertise lies in the latest version of Spring Framework, Spring Boot, Spring Security, creating REST APIs, Microservice Architecture, Reactive Pattern, Spring AOP, Design Patterns, Struts, Hibernate, Web Services, Spring Batch, Cassandra, MongoDB, and Web Application Design and Architecture. He is currently working as a technology manager at a leading product and web development company. He worked as a developer and tech lead at the Bennett, Coleman & Co. Ltd and was the first developer in his previous company, Paytm. Dinesh is passionate about the latest Java technologies and loves to write technical blogs related to it. He is a very active member of the Java and Spring community on different forums. When it comes to the Spring Framework and Java, Dinesh tops the list!

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