Print Nodes at K distance from Root in Binary Tree

Print nodes at K distance from root in binary tree. OR
Print nodes at Level K.

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Given a Binary Tree, Print all Nodes that are at K distance from root node in Binary Tree. We can also think of this question as Print all nodes that belong to Level K.
 
Lets understand what will be input and expected output with the help of an example.
 

If k = 2. It means we need to print all nodes that are at distance 2 from Root node.
It also means we need to print all nodes at Level 2, because all Nodes of Level 2 will be at same distance from Root Node.

Algorithm

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We already saw how to Printing nodes at K distance from Leaf node in Binary tree.

Print Nodes at K distance from Root in Binary Tree is very easy and just require Pre-order traversal of Tree.
If you are not familar with Pre order traversal, I would suggest to have a look at Pre-order traversal first: Pre-Order Traversal of Binary Tree

1. Do a Pre-Order traversal of Tree and and decrement K each time you move to left or right.
2. When K = 0, it means that is the level we are interested in.
   So print the Node and return.

Note:  Once we reach k = 0, no need to further explore the tree down, because we already reached the level that we are interested in, So going ahead is of no use.

Java Program to Print Nodes at K distance from Root.

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package javabypatel;

public class PrintNodesAtKDistanceFromRoot {

 public static void main(String[] args) {
  new PrintNodesAtKDistanceFromRoot();
 }

 public PrintNodesAtKDistanceFromRoot(){

  Node rootNode=null; 
  rootNode  = addNode(rootNode, 50);
  rootNode  = addNode(rootNode, 30);
  rootNode  = addNode(rootNode, 70);
  rootNode  = addNode(rootNode, 20);
  rootNode  = addNode(rootNode, 40);
  rootNode  = addNode(rootNode, 10);
  rootNode  = addNode(rootNode, 25);
  rootNode  = addNode(rootNode, 60);
  rootNode  = addNode(rootNode, 80);
  

  printNodesAtLevel(rootNode, 0);
 }

 private void printNodesAtLevel(Node rootNode, int level) {
  if(rootNode==null){
   return;
  }
  
  if(level == 0){
   System.out.print(rootNode.getData() + " ");
   return;
  }
  
  printNodesAtLevel(rootNode.getLeft(), level - 1);
  printNodesAtLevel(rootNode.getRight(), level - 1);
 }

 private Node addNode(Node rootNode, int i) {
  if(rootNode==null){
   return new Node(i);
  }else{
   if(i > rootNode.getData()){
    Node nodeToAdd = addNode(rootNode.getRight(), i);
    rootNode.setRight(nodeToAdd);

   }else{
    Node nodeToAdd = addNode(rootNode.getLeft(), i);
    rootNode.setLeft(nodeToAdd);
   }
  }
  return rootNode;
 }
}

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Top Binary tree interview questions in Java

Find Kth SMALLEST element in BST(Binary Search Tree)

Check whether Binary Tree is foldable or not.

Check if two nodes are cousins in a Binary Tree.

Get Level/Height of node in binary tree

Print nodes at K distance from Leaf node in Binary tree.

Construct a Binary Tree from In-order and Post-order traversals.

Print Nodes in Top View of Binary Tree.

Zig Zag Traversal of Binary Tree.

Advanced Multithreading Interview Questions In Java

Enjoy !!!! 

If you find any issue in post or face any error while implementing, Please comment.