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Print all nodes between the given two levels of a binary tree

In this problem, we are given a binary tree, and we are required to print all the nodes that lie between two given levels, inclusive of those levels. The binary tree is a data structure where each node can have at most two children, referred to as the left child and the right child.

Example

Consider the following binary tree:


       10
     /   \
    2     3
   /     / \
  4     9   5
 /  \    \    \
7    3    6   20
    /  \     /
   2    8   -3
         \    
          9

Nodes between levels 2 and 4 (inclusive) are: 2, 3, 4, 9, 5, 7, 3, 6, 20

Nodes between levels 4 and 6 (inclusive) are: 7, 3, 6, 20, 2, 8, -3, 9

Nodes between levels 1 and 3 (inclusive) are: 10, 2, 3, 4, 9, 5

Nodes between levels 7 and 8 (inclusive) are: None (as there are no nodes in these levels)

Idea to Solve the Problem

To print the nodes between two given levels, we can perform a level order traversal of the binary tree using a custom queue data structure. For each level, we check if it falls between the given levels (inclusive) and print the nodes accordingly.

Code Solution

// C program
// Print all nodes between the given two levels of a binary tree
#include <stdio.h>

#include <stdlib.h>

//Node of binary tree
struct Node
{
	int data;
	struct Node *left, *right;
};
struct MyQueue
{
	int level;
	struct Node *element;
	struct MyQueue *next;
};
//Create a binary tree nodes and node fields (data,pointer) 
//And returning the reference of newly nodes
struct Node *insert(int data)
{
	//create dynamic memory to new binary tree node
	struct Node *new_node = (struct Node *) malloc(sizeof(struct Node));
	if (new_node != NULL)
	{
		//Set node value
		new_node->data = data;
		new_node->left = NULL;
		new_node->right = NULL;
	}
	else
	{
		printf("Memory Overflow\n");
	}
	//return reference
	return new_node;
}
//Create a queue node and returns this node
struct MyQueue *enqueue(struct Node *tree_node)
{
	//Make a new Queue node
	struct MyQueue *new_node = (struct MyQueue *) malloc(sizeof(struct MyQueue));
	if (new_node != NULL)
	{
		//Set node values
		new_node->element = tree_node;
		new_node->next = NULL;
	}
	else
	{
		printf("Memory Overflow\n");
	}
	return new_node;
}
//Remove a queue elements
void dequeue(struct MyQueue **front)
{
	if ( *front != NULL)
	{
		struct MyQueue *remove = *front;
		//Visit to next node
		*front = remove->next;
		remove->element = NULL;
		remove->next = NULL;
		//free node
		free(remove);
		remove = NULL;
	}
}
//This are printing all binary tree nodes, between given (A to B) levels
void print_level_nodes(struct Node *root, int a, int b)
{
	if (a <= 0 || b <= 0)
	{
		//invalid level
		return;
	}
	if (a > b)
	{
		//When level sequence in not valid
		//Then change its sequence
		print_level_nodes(root, b, a);
	}
	else
	{
		if (root != NULL)
		{
			//make a queue pointers
			struct MyQueue *front = NULL, *tail = NULL;
			//Get first node of tree
			front = enqueue(root);
			//Start level of first node is one
			front->level = 1;
			//Set tail node to first node
			tail = front;
			printf("\n Node between level (%d-%d) is \n", a, b);
			// Define a tree variable
			struct Node *node = NULL;
			// Result indicator
			int status = 0;
			// Traversal tree elements in level order
			while (front != NULL)
			{
				// Tree node
				node = front->element;
				if (node->left != NULL)
				{
					// Add new left child node
					tail->next = enqueue(node->left);
					tail->next->level = front->level + 1;
					tail = tail->next;
				}
				if (node->right != NULL)
				{
					// Add new right child node
					tail->next = enqueue(node->right);
					tail->next->level = front->level + 1;
					tail = tail->next;
				}
				if (front->level >= a && front->level <= b)
				{
					printf(" %d", node->data);
					status = 1;
				}
				dequeue( &front);
			}
			tail = NULL;
			if (status == 0)
			{
				printf(" None");
			}
		}
		else
		{
			printf("\nEmpty Tree\n");
		}
	}
}
int main()
{
	struct Node *root = NULL;
	/*
	Construct Binary Tree
	-----------------------
	       10
	     /   \
	    2     3
	   /     / \
	  4     9   5
	 /  \    \    \
	7    3    6   20
	    /  \     /
	   2    8   -3
	         \    
	          9
	-----------------------
	*/
	//Add node
	root = insert(10);
	root->left = insert(2);
	root->right = insert(3);
	root->right->right = insert(5);
	root->right->left = insert(9);
	root->left->left = insert(4);
	root->left->left->left = insert(7);
	root->left->left->right = insert(3);
	root->right->left->right = insert(6);
	root->right->right->right = insert(20);
	root->right->right->right->left = insert(-3);
	root->left->left->right->left = insert(2);
	root->left->left->right->right = insert(8);
	root->left->left->right->right->right = insert(9);
	print_level_nodes(root, 2, 4);
	print_level_nodes(root, 4, 6);
	print_level_nodes(root, 1, 3);
	print_level_nodes(root, 7, 8);
	return 0;
}

Output

 Node between level (2-4) is
 2 3 4 9 5 7 3 6 20
 Node between level (4-6) is
 7 3 6 20 2 8 -3 9
 Node between level (1-3) is
 10 2 3 4 9 5
 Node between level (7-8) is
 None
/* 
  Java program 
  Print all palindromic levels of a binary tree
*/
//Binary Tree node
class TreeNode
{
	public int data;
	public TreeNode left;
	public TreeNode right;
	public TreeNode(int data)
	{
		//set node value
		this.data = data;
		this.left = null;
		this.right = null;
	}
}
// Queue Node
class QueueNode
{
	public TreeNode element;
	public QueueNode next;
	public int level;
	public QueueNode(TreeNode element, int level)
	{
		this.element = element;
		this.next = null;
		this.level = level;
	}
}
//Define custom queue class
class MyQueue
{
	public QueueNode front;
	public QueueNode tail;
	public MyQueue()
	{
		this.front = null;
		this.tail = null;
	}
	//Add a new node at last of queue
	public void enqueue(TreeNode element, int level)
	{
		QueueNode new_node = new QueueNode(element, level);
		if (this.front == null)
		{
			//When first node of queue
			this.front = new_node;
		}
		else
		{
			//Add node at last position
			this.tail.next = new_node;
		}
		this.tail = new_node;
	}
	//Delete first node of queue
	public void dequeue()
	{
		if (this.front != null)
		{
			if (this.tail == this.front)
			{
				this.tail = null;
				this.front = null;
			}
			else
			{
				this.front = this.front.next;
			}
		}
	}
	public boolean is_empty()
	{
		if (this.front == null)
		{
			return true;
		}
		else
		{
			return false;
		}
	}
}
class BinaryTree
{
	public TreeNode root;
	public BinaryTree()
	{
		// Set initial tree root to null
		this.root = null;
	}
	// This are printing all binary tree nodes, between given (A to B) levels
	public void print_level_nodes(int a, int b)
	{
		if (this.root == null)
		{
			System.out.print("\n Empty Binary Tree \n");
		}
		else
		{
			//Get top node in tree
			TreeNode node = this.root;
			int level = 1;
			//Create a Queue
			MyQueue queue = new MyQueue();
			//Add first node at the level of one
			queue.enqueue(node, level);
			System.out.print("\n Node between level (" + a + "-" + b + ") is \n");
			// Result indicator
			boolean status = false;
			//Execute loop until the queue is not empty
			while (queue.is_empty() == false)
			{
				node = queue.front.element;
				level = queue.front.level;
				if (node.left != null)
				{
					//Add left node
					queue.enqueue(node.left, level + 1);
				}
				if (node.right != null)
				{
					//Add right node
					queue.enqueue(node.right, level + 1);
				}
				if (level >= a && level <= b)
				{
					status = true;
					System.out.print("  " + node.data);
				}
				//remove element into queue
				queue.dequeue();
			}
          	if(status==false)
            {
            	System.out.print(" None\n");
            }
		}
	}
	public static void main(String[] args)
	{
		//Object of Binary Tree
		BinaryTree tree = new BinaryTree();
		/*  
		Construct Binary Tree
		-----------------------
		       10
		     /   \
		    2     3
		   /     / \
		  4     9   5
		 /  \    \    \
		7    3    6   20
		    /  \     /
		   2    8   -3
		         \    
		          9
		-----------------------
		*/
		//Add node
		tree.root = new TreeNode(10);
		tree.root.left = new TreeNode(2);
		tree.root.right = new TreeNode(3);
		tree.root.right.right = new TreeNode(5);
		tree.root.right.left = new TreeNode(9);
		tree.root.left.left = new TreeNode(4);
		tree.root.left.left.left = new TreeNode(7);
		tree.root.left.left.right = new TreeNode(3);
		tree.root.right.left.right = new TreeNode(6);
		tree.root.right.right.right = new TreeNode(20);
		tree.root.right.right.right.left = new TreeNode(-3);
		tree.root.left.left.right.left = new TreeNode(2);
		tree.root.left.left.right.right = new TreeNode(8);
		tree.root.left.left.right.right.right = new TreeNode(9);
		tree.print_level_nodes(2, 4);
		tree.print_level_nodes(4, 6);
		tree.print_level_nodes(1, 3);
		tree.print_level_nodes(7, 8);
	}
}

Output

 Node between level (2-4) is
  2  3  4  9  5  7  3  6  20
 Node between level (4-6) is
  7  3  6  20  2  8  -3  9
 Node between level (1-3) is
  10  2  3  4  9  5
 Node between level (7-8) is
 None
//Include header file
#include <iostream>
using namespace std;

/*
  C++ program 
  Print all palindromic levels of a binary tree
*/

//Binary Tree node
class TreeNode
{
	public: int data;
	TreeNode *left;
	TreeNode *right;
	TreeNode(int data)
	{
		//set node value
		this->data = data;
		this->left = NULL;
		this->right = NULL;
	}
};
// Queue Node
class QueueNode
{
	public: TreeNode *element;
	QueueNode *next;
	int level;
	QueueNode(TreeNode *element, int level)
	{
		this->element = element;
		this->next = NULL;
		this->level = level;
	}
};
//Define custom queue class
class MyQueue
{
	public: QueueNode *front;
	QueueNode *tail;
	MyQueue()
	{
		this->front = NULL;
		this->tail = NULL;
	}
	//Add a new node at last of queue
	void enqueue(TreeNode *element, int level)
	{
		QueueNode *new_node = new QueueNode(element, level);
		if (this->front == NULL)
		{
			//When first node of queue
			this->front = new_node;
		}
		else
		{
			//Add node at last position
			this->tail->next = new_node;
		}
		this->tail = new_node;
	}
	//Delete first node of queue
	void dequeue()
	{
		if (this->front != NULL)
		{
			if (this->tail == this->front)
			{
				this->tail = NULL;
				this->front = NULL;
			}
			else
			{
				this->front = this->front->next;
			}
		}
	}
	bool is_empty()
	{
		if (this->front == NULL)
		{
			return true;
		}
		else
		{
			return false;
		}
	}
};
class BinaryTree
{
	public: TreeNode *root;
	BinaryTree()
	{
		// Set initial tree root to null
		this->root = NULL;
	}
	// This are printing all binary tree nodes, between given (A to B) levels
	void print_level_nodes(int a, int b)
	{
		if (this->root == NULL)
		{
			cout << "\n Empty Binary Tree \n";
		}
		else
		{
			//Get top node in tree
			TreeNode *node = this->root;
			int level = 1;
			//Create a Queue
			MyQueue queue = MyQueue();
			//Add first node at the level of one
			queue.enqueue(node, level);
			cout << "\n Node between level (" << a << "-" << b << ") is \n";
			// Result indicator
			bool status = false;
			//Execute loop until the queue is not empty
			while (queue.is_empty() == false)
			{
				node  = queue.front->element;
				level = queue.front->level;
				if (node->left != NULL)
				{
					//Add left node
					queue.enqueue(node->left, level + 1);
				}
				if (node->right != NULL)
				{
					//Add right node
					queue.enqueue(node->right, level + 1);
				}
				if (level >= a && level <= b)
				{
					status = true;
					cout << "  " << node->data;
				}
				//remove element into queue
				queue.dequeue();
			}
			if (status == false)
			{
				cout << " None\n";
			}
		}
	}
};
int main()
{
	//Object of Binary Tree
	BinaryTree tree = BinaryTree();
	tree.root = new TreeNode(10);
	tree.root->left = new TreeNode(2);
	tree.root->right = new TreeNode(3);
	tree.root->right->right = new TreeNode(5);
	tree.root->right->left = new TreeNode(9);
	tree.root->left->left = new TreeNode(4);
	tree.root->left->left->left = new TreeNode(7);
	tree.root->left->left->right = new TreeNode(3);
	tree.root->right->left->right = new TreeNode(6);
	tree.root->right->right->right = new TreeNode(20);
	tree.root->right->right->right->left = new TreeNode(-3);
	tree.root->left->left->right->left = new TreeNode(2);
	tree.root->left->left->right->right = new TreeNode(8);
	tree.root->left->left->right->right->right = new TreeNode(9);
	tree.print_level_nodes(2, 4);
	tree.print_level_nodes(4, 6);
	tree.print_level_nodes(1, 3);
	tree.print_level_nodes(7, 8);
	return 0;
}

Output

 Node between level (2-4) is
  2  3  4  9  5  7  3  6  20
 Node between level (4-6) is
  7  3  6  20  2  8  -3  9
 Node between level (1-3) is
  10  2  3  4  9  5
 Node between level (7-8) is
 None
//Include namespace system
using System;

/* 
  C# program 
  Print all palindromic levels of a binary tree
*/

//Binary Tree node
class TreeNode
{
	public int data;
	public TreeNode left;
	public TreeNode right;
	public TreeNode(int data)
	{
		//set node value
		this.data = data;
		this.left = null;
		this.right = null;
	}
}
// Queue Node
class QueueNode
{
	public TreeNode element;
	public QueueNode next;
	public int level;
	public QueueNode(TreeNode element, int level)
	{
		this.element = element;
		this.next = null;
		this.level = level;
	}
}
//Define custom queue class
class MyQueue
{
	public QueueNode front;
	public QueueNode tail;
	public MyQueue()
	{
		this.front = null;
		this.tail = null;
	}
	//Add a new node at last of queue
	public void enqueue(TreeNode element, int level)
	{
		QueueNode new_node = new QueueNode(element, level);
		if (this.front == null)
		{
			//When first node of queue
			this.front = new_node;
		}
		else
		{
			//Add node at last position
			this.tail.next = new_node;
		}
		this.tail = new_node;
	}
	//Delete first node of queue
	public void dequeue()
	{
		if (this.front != null)
		{
			if (this.tail == this.front)
			{
				this.tail = null;
				this.front = null;
			}
			else
			{
				this.front = this.front.next;
			}
		}
	}
	public Boolean is_empty()
	{
		if (this.front == null)
		{
			return true;
		}
		else
		{
			return false;
		}
	}
}
class BinaryTree
{
	public TreeNode root;
	public BinaryTree()
	{
		// Set initial tree root to null
		this.root = null;
	}
	// This are printing all binary tree nodes, between given (A to B) levels
	public void print_level_nodes(int a, int b)
	{
		if (this.root == null)
		{
			Console.Write("\n Empty Binary Tree \n");
		}
		else
		{
			//Get top node in tree
			TreeNode node = this.root;
			int level = 1;
			//Create a Queue
			MyQueue queue = new MyQueue();
			//Add first node at the level of one
			queue.enqueue(node, level);
			Console.Write("\n Node between level (" + a + "-" + b + ") is \n");
			// Result indicator
			Boolean status = false;
			//Execute loop until the queue is not empty
			while (queue.is_empty() == false)
			{
				node = queue.front.element;
				level = queue.front.level;
				if (node.left != null)
				{
					//Add left node
					queue.enqueue(node.left, level + 1);
				}
				if (node.right != null)
				{
					//Add right node
					queue.enqueue(node.right, level + 1);
				}
				if (level >= a && level <= b)
				{
					status = true;
					Console.Write("  " + node.data);
				}
				//remove element into queue
				queue.dequeue();
			}
			if (status == false)
			{
				Console.Write(" None\n");
			}
		}
	}
	public static void Main(String[] args)
	{
		//Object of Binary Tree
		BinaryTree tree = new BinaryTree();
		tree.root = new TreeNode(10);
		tree.root.left = new TreeNode(2);
		tree.root.right = new TreeNode(3);
		tree.root.right.right = new TreeNode(5);
		tree.root.right.left = new TreeNode(9);
		tree.root.left.left = new TreeNode(4);
		tree.root.left.left.left = new TreeNode(7);
		tree.root.left.left.right = new TreeNode(3);
		tree.root.right.left.right = new TreeNode(6);
		tree.root.right.right.right = new TreeNode(20);
		tree.root.right.right.right.left = new TreeNode(-3);
		tree.root.left.left.right.left = new TreeNode(2);
		tree.root.left.left.right.right = new TreeNode(8);
		tree.root.left.left.right.right.right = new TreeNode(9);
		tree.print_level_nodes(2, 4);
		tree.print_level_nodes(4, 6);
		tree.print_level_nodes(1, 3);
		tree.print_level_nodes(7, 8);
	}
}

Output

 Node between level (2-4) is
  2  3  4  9  5  7  3  6  20
 Node between level (4-6) is
  7  3  6  20  2  8  -3  9
 Node between level (1-3) is
  10  2  3  4  9  5
 Node between level (7-8) is
 None
<?php
/* 
  Php program 
  Print all palindromic levels of a binary tree
*/

//Binary Tree node
class TreeNode
{
	public $data;
	public $left;
	public $right;

	function __construct($data)
	{
		//set node value
		$this->data = $data;
		$this->left = null;
		$this->right = null;
	}
}
// Queue Node
class QueueNode
{
	public $element;
	public $next;
	public $level;

	function __construct($element, $level)
	{
		$this->element = $element;
		$this->next = null;
		$this->level = $level;
	}
}
//Define custom queue class
class MyQueue
{
	public $front;
	public $tail;

	function __construct()
	{
		$this->front = null;
		$this->tail = null;
	}
	//Add a new node at last of queue
	public	function enqueue($element, $level)
	{
		$new_node = new QueueNode($element, $level);
		if ($this->front == null)
		{
			//When first node of queue
			$this->front = $new_node;
		}
		else
		{
			//Add node at last position
			$this->tail->next = $new_node;
		}
		$this->tail = $new_node;
	}
	//Delete first node of queue
	public	function dequeue()
	{
		if ($this->front != null)
		{
			if ($this->tail == $this->front)
			{
				$this->tail = null;
				$this->front = null;
			}
			else
			{
				$this->front = $this->front->next;
			}
		}
	}
	public	function is_empty()
	{
		if ($this->front == null)
		{
			return true;
		}
		else
		{
			return false;
		}
	}
}
class BinaryTree
{
	public $root;

	function __construct()
	{
		// Set initial tree root to null
		$this->root = null;
	}
	// This are printing all binary tree nodes, between given (A to B) levels
	public	function print_level_nodes($a, $b)
	{
		if ($this->root == null)
		{
			echo "\n Empty Binary Tree \n";
		}
		else
		{
			//Get top node in tree
			$node = $this->root;
			$level = 1;
			//Create a Queue
			$queue = new MyQueue();
			//Add first node at the level of one
			$queue->enqueue($node, $level);
			echo "\n Node between level (". $a ."-". $b .") is \n";
			// Result indicator
			$status = false;
			//Execute loop until the queue is not empty
			while ($queue->is_empty() == false)
			{
				$node = $queue->front->element;
				$level = $queue->front->level;
				if ($node->left != null)
				{
					//Add left node
					$queue->enqueue($node->left, $level + 1);
				}
				if ($node->right != null)
				{
					//Add right node
					$queue->enqueue($node->right, $level + 1);
				}
				if ($level >= $a && $level <= $b)
				{
					$status = true;
					echo "  ". $node->data;
				}
				//remove element into queue
				$queue->dequeue();
			}
			if ($status == false)
			{
				echo " None\n";
			}
		}
	}
}

function main()
{
	//Object of Binary Tree
	$tree = new BinaryTree();
	/*  
			Construct Binary Tree
			-----------------------
			       10
			     /   \
			    2     3
			   /     / \
			  4     9   5
			 /  \    \    \
			7    3    6   20
			    /  \     /
			   2    8   -3
			         \    
			          9
			-----------------------
			*/
	//Add node
	$tree->root = new TreeNode(10);
	$tree->root->left = new TreeNode(2);
	$tree->root->right = new TreeNode(3);
	$tree->root->right->right = new TreeNode(5);
	$tree->root->right->left = new TreeNode(9);
	$tree->root->left->left = new TreeNode(4);
	$tree->root->left->left->left = new TreeNode(7);
	$tree->root->left->left->right = new TreeNode(3);
	$tree->root->right->left->right = new TreeNode(6);
	$tree->root->right->right->right = new TreeNode(20);
	$tree->root->right->right->right->left = new TreeNode(-3);
	$tree->root->left->left->right->left = new TreeNode(2);
	$tree->root->left->left->right->right = new TreeNode(8);
	$tree->root->left->left->right->right->right = new TreeNode(9);
	$tree->print_level_nodes(2, 4);
	$tree->print_level_nodes(4, 6);
	$tree->print_level_nodes(1, 3);
	$tree->print_level_nodes(7, 8);
}
main();

Output

 Node between level (2-4) is
  2  3  4  9  5  7  3  6  20
 Node between level (4-6) is
  7  3  6  20  2  8  -3  9
 Node between level (1-3) is
  10  2  3  4  9  5
 Node between level (7-8) is
 None
/* 
  Node Js program 
  Print all palindromic levels of a binary tree
*/

//Binary Tree node
class TreeNode
{
	constructor(data)
	{
		//set node value
		this.data = data;
		this.left = null;
		this.right = null;
	}
}
// Queue Node
class QueueNode
{
	constructor(element, level)
	{
		this.element = element;
		this.next = null;
		this.level = level;
	}
}
//Define custom queue class
class MyQueue
{
	constructor()
	{
		this.front = null;
		this.tail = null;
	}
	//Add a new node at last of queue
	enqueue(element, level)
	{
		var new_node = new QueueNode(element, level);
		if (this.front == null)
		{
			//When first node of queue
			this.front = new_node;
		}
		else
		{
			//Add node at last position
			this.tail.next = new_node;
		}
		this.tail = new_node;
	}
	//Delete first node of queue
	dequeue()
	{
		if (this.front != null)
		{
			if (this.tail == this.front)
			{
				this.tail = null;
				this.front = null;
			}
			else
			{
				this.front = this.front.next;
			}
		}
	}
	is_empty()
	{
		if (this.front == null)
		{
			return true;
		}
		else
		{
			return false;
		}
	}
}
class BinaryTree
{
	constructor()
	{
		// Set initial tree root to null
		this.root = null;
	}
	// This are printing all binary tree nodes, between given (A to B) levels
	print_level_nodes(a, b)
	{
		if (this.root == null)
		{
			process.stdout.write("\n Empty Binary Tree \n");
		}
		else
		{
			//Get top node in tree
			var node = this.root;
			var level = 1;
			//Create a Queue
			var queue = new MyQueue();
			//Add first node at the level of one
			queue.enqueue(node, level);
			process.stdout.write("\n Node between level (" + a + "-" + b + ") is \n");
			// Result indicator
			var status = false;
			//Execute loop until the queue is not empty
			while (queue.is_empty() == false)
			{
				node = queue.front.element;
				level = queue.front.level;
				if (node.left != null)
				{
					//Add left node
					queue.enqueue(node.left, level + 1);
				}
				if (node.right != null)
				{
					//Add right node
					queue.enqueue(node.right, level + 1);
				}
				if (level >= a && level <= b)
				{
					status = true;
					process.stdout.write("  " + node.data);
				}
				//remove element into queue
				queue.dequeue();
			}
			if (status == false)
			{
				process.stdout.write(" None\n");
			}
		}
	}
}

function main()
{
	//Object of Binary Tree
	var tree = new BinaryTree();
	/*  
			Construct Binary Tree
			-----------------------
			       10
			     /   \
			    2     3
			   /     / \
			  4     9   5
			 /  \    \    \
			7    3    6   20
			    /  \     /
			   2    8   -3
			         \    
			          9
			-----------------------
			*/
	//Add node
	tree.root = new TreeNode(10);
	tree.root.left = new TreeNode(2);
	tree.root.right = new TreeNode(3);
	tree.root.right.right = new TreeNode(5);
	tree.root.right.left = new TreeNode(9);
	tree.root.left.left = new TreeNode(4);
	tree.root.left.left.left = new TreeNode(7);
	tree.root.left.left.right = new TreeNode(3);
	tree.root.right.left.right = new TreeNode(6);
	tree.root.right.right.right = new TreeNode(20);
	tree.root.right.right.right.left = new TreeNode(-3);
	tree.root.left.left.right.left = new TreeNode(2);
	tree.root.left.left.right.right = new TreeNode(8);
	tree.root.left.left.right.right.right = new TreeNode(9);
	tree.print_level_nodes(2, 4);
	tree.print_level_nodes(4, 6);
	tree.print_level_nodes(1, 3);
	tree.print_level_nodes(7, 8);
}
main();

Output

 Node between level (2-4) is
  2  3  4  9  5  7  3  6  20
 Node between level (4-6) is
  7  3  6  20  2  8  -3  9
 Node between level (1-3) is
  10  2  3  4  9  5
 Node between level (7-8) is
 None
#   Python 3 program 
#   Print all palindromic levels of a binary tree

# Binary Tree node
class TreeNode :
	
	def __init__(self, data) :
		# set node value
		self.data = data
		self.left = None
		self.right = None
	

#  Queue Node
class QueueNode :
	
	def __init__(self, element, level) :
		self.element = element
		self.next = None
		self.level = level
	

# Define custom queue class
class MyQueue :
	
	def __init__(self) :
		self.front = None
		self.tail = None
	
	# Add a new node at last of queue
	def enqueue(self, element, level) :
		new_node = QueueNode(element, level)
		if (self.front == None) :
			# When first node of queue
			self.front = new_node
		else :
			# Add node at last position
			self.tail.next = new_node
		
		self.tail = new_node
	
	# Delete first node of queue
	def dequeue(self) :
		if (self.front != None) :
			if (self.tail == self.front) :
				self.tail = None
				self.front = None
			else :
				self.front = self.front.next
			
		
	
	def is_empty(self) :
		if (self.front == None) :
			return True
		else :
			return False
		
	

class BinaryTree :
	
	def __init__(self) :
		#  Set initial tree root to null
		self.root = None
	
	#  This are printing all binary tree nodes, between given (A to B) levels
	def print_level_nodes(self, a, b) :
		if (self.root == None) :
			print("\n Empty Binary Tree \n", end = "")
		else :
			# Get top node in tree
			node = self.root
			level = 1
			# Create a Queue
			queue = MyQueue()
			# Add first node at the level of one
			queue.enqueue(node, level)
			print("\n Node between level (", a ,"-", b ,") is \n", end = "")
			#  Result indicator
			status = False
			# Execute loop until the queue is not empty
			while (queue.is_empty() == False) :
				node = queue.front.element
				level = queue.front.level
				if (node.left != None) :
					# Add left node
					queue.enqueue(node.left, level + 1)
				
				if (node.right != None) :
					# Add right node
					queue.enqueue(node.right, level + 1)
				
				if (level >= a and level <= b) :
					status = True
					print("  ", node.data, end = "")
				
				# remove element into queue
				queue.dequeue()
			
			if (status == False) :
				print(" None\n", end = "")
			
		
	

def main() :
	# Object of Binary Tree
	tree = BinaryTree()
	#   
	# 		Construct Binary Tree
	# 		-----------------------
	# 		       10
	# 		     /   \
	# 		    2     3
	# 		   /     / \
	# 		  4     9   5
	# 		 /  \    \    \
	# 		7    3    6   20
	# 		    /  \     /
	# 		   2    8   -3
	# 		         \    
	# 		          9
	# 		-----------------------
	# 		
	
	# Add node
	tree.root = TreeNode(10)
	tree.root.left = TreeNode(2)
	tree.root.right = TreeNode(3)
	tree.root.right.right = TreeNode(5)
	tree.root.right.left = TreeNode(9)
	tree.root.left.left = TreeNode(4)
	tree.root.left.left.left = TreeNode(7)
	tree.root.left.left.right = TreeNode(3)
	tree.root.right.left.right = TreeNode(6)
	tree.root.right.right.right = TreeNode(20)
	tree.root.right.right.right.left = TreeNode(-3)
	tree.root.left.left.right.left = TreeNode(2)
	tree.root.left.left.right.right = TreeNode(8)
	tree.root.left.left.right.right.right = TreeNode(9)
	tree.print_level_nodes(2, 4)
	tree.print_level_nodes(4, 6)
	tree.print_level_nodes(1, 3)
	tree.print_level_nodes(7, 8)

if __name__ == "__main__": main()

Output

 Node between level ( 2 - 4 ) is
   2   3   4   9   5   7   3   6   20
 Node between level ( 4 - 6 ) is
   7   3   6   20   2   8   -3   9
 Node between level ( 1 - 3 ) is
   10   2   3   4   9   5
 Node between level ( 7 - 8 ) is
 None
#   Ruby program 
#   Print all palindromic levels of a binary tree

# Binary Tree node
class TreeNode  
	# Define the accessor and reader of class TreeNode  
	attr_reader :data, :left, :right
	attr_accessor :data, :left, :right
 
	
	def initialize(data) 
		# set node value
		self.data = data
		self.left = nil
		self.right = nil
	end

end

#  Queue Node
class QueueNode  
	# Define the accessor and reader of class QueueNode  
	attr_reader :element, :next, :level
	attr_accessor :element, :next, :level
 
	
	def initialize(element, level) 
		self.element = element
		self.next = nil
		self.level = level
	end

end

# Define custom queue class
class MyQueue  
	# Define the accessor and reader of class MyQueue  
	attr_reader :front, :tail
	attr_accessor :front, :tail
 
	
	def initialize() 
		self.front = nil
		self.tail = nil
	end

	# Add a new node at last of queue
	def enqueue(element, level) 
		new_node = QueueNode.new(element, level)
		if (self.front == nil) 
			# When first node of queue
			self.front = new_node
		else 
			# Add node at last position
			self.tail.next = new_node
		end

		self.tail = new_node
	end

	# Delete first node of queue
	def dequeue() 
		if (self.front != nil) 
			if (self.tail == self.front) 
				self.tail = nil
				self.front = nil
			else 
				self.front = self.front.next
			end

		end

	end

	def is_empty() 
		if (self.front == nil) 
			return true
		else 
			return false
		end

	end

end

class BinaryTree  
	# Define the accessor and reader of class BinaryTree  
	attr_reader :root
	attr_accessor :root
 
	
	def initialize() 
		#  Set initial tree root to null
		self.root = nil
	end

	#  This are printing all binary tree nodes, between given (A to B) levels
	def print_level_nodes(a, b) 
		if (self.root == nil) 
			print("\n Empty Binary Tree \n")
		else 
			# Get top node in tree
			node = self.root
			level = 1
			# Create a Queue
			queue = MyQueue.new()
			# Add first node at the level of one
			queue.enqueue(node, level)
			print("\n Node between level (", a ,"-", b ,") is \n")
			#  Result indicator
			status = false
			# Execute loop until the queue is not empty
			while (queue.is_empty() == false) 
				node = queue.front.element
				level = queue.front.level
				if (node.left != nil) 
					# Add left node
					queue.enqueue(node.left, level + 1)
				end

				if (node.right != nil) 
					# Add right node
					queue.enqueue(node.right, level + 1)
				end

				if (level >= a && level <= b) 
					status = true
					print("  ", node.data)
				end

				# remove element into queue
				queue.dequeue()
			end

			if (status == false) 
				print(" None\n")
			end

		end

	end

end

def main() 
	# Object of Binary Tree
	tree = BinaryTree.new()
	#   
	# 		Construct Binary Tree
	# 		-----------------------
	# 		       10
	# 		     /   \
	# 		    2     3
	# 		   /     / \
	# 		  4     9   5
	# 		 /  \    \    \
	# 		7    3    6   20
	# 		    /  \     /
	# 		   2    8   -3
	# 		         \    
	# 		          9
	# 		-----------------------
	# 		
	
	# Add node
	tree.root = TreeNode.new(10)
	tree.root.left = TreeNode.new(2)
	tree.root.right = TreeNode.new(3)
	tree.root.right.right = TreeNode.new(5)
	tree.root.right.left = TreeNode.new(9)
	tree.root.left.left = TreeNode.new(4)
	tree.root.left.left.left = TreeNode.new(7)
	tree.root.left.left.right = TreeNode.new(3)
	tree.root.right.left.right = TreeNode.new(6)
	tree.root.right.right.right = TreeNode.new(20)
	tree.root.right.right.right.left = TreeNode.new(-3)
	tree.root.left.left.right.left = TreeNode.new(2)
	tree.root.left.left.right.right = TreeNode.new(8)
	tree.root.left.left.right.right.right = TreeNode.new(9)
	tree.print_level_nodes(2, 4)
	tree.print_level_nodes(4, 6)
	tree.print_level_nodes(1, 3)
	tree.print_level_nodes(7, 8)
end

main()

Output

 Node between level (2-4) is 
  2  3  4  9  5  7  3  6  20
 Node between level (4-6) is 
  7  3  6  20  2  8  -3  9
 Node between level (1-3) is 
  10  2  3  4  9  5
 Node between level (7-8) is 
 None
/* 
  Scala program 
  Print all palindromic levels of a binary tree
*/

//Binary Tree node
class TreeNode(var data: Int,
	var left: TreeNode,
		var right: TreeNode)
{
	def this(data: Int)
	{
		this(data, null, null);
	}
}
// Queue Node
class QueueNode(var element: TreeNode,
	var next: QueueNode,
		var level: Int)
{
	def this(element: TreeNode, level: Int)
	{
		this(element, null, level);
	}
}
//Define custom queue class
class MyQueue(var front: QueueNode,
	var tail: QueueNode)
{
	def this()
	{
		this(null, null);
	}
	//Add a new node at last of queue
	def enqueue(element: TreeNode, level: Int): Unit = {
		var new_node: QueueNode = new QueueNode(element, level);
		if (this.front == null)
		{
			//When first node of queue
			this.front = new_node;
		}
		else
		{
			//Add node at last position
			this.tail.next = new_node;
		}
		this.tail = new_node;
	}
	//Delete first node of queue
	def dequeue(): Unit = {
		if (this.front != null)
		{
			if (this.tail == this.front)
			{
				this.tail = null;
				this.front = null;
			}
			else
			{
				this.front = this.front.next;
			}
		}
	}
	def is_empty(): Boolean = {
		if (this.front == null)
		{
			return true;
		}
		else
		{
			return false;
		}
	}
}
class BinaryTree(var root: TreeNode)
{
	def this()
	{
		this(null);
	}
	// This are printing all binary tree nodes, between given (A to B) levels
	def print_level_nodes(a: Int, b: Int): Unit = {
		if (this.root == null)
		{
			print("\n Empty Binary Tree \n");
		}
		else
		{
			//Get top node in tree
			var node: TreeNode = this.root;
			var level: Int = 1;
			//Create a Queue
			var queue: MyQueue = new MyQueue();
			//Add first node at the level of one
			queue.enqueue(node, level);
			print("\n Node between level (" + a + "-" + b + ") is \n");
			// Result indicator
			var status: Boolean = false;
			//Execute loop until the queue is not empty
			while (queue.is_empty() == false)
			{
				node = queue.front.element;
				level = queue.front.level;
				if (node.left != null)
				{
					//Add left node
					queue.enqueue(node.left, level + 1);
				}
				if (node.right != null)
				{
					//Add right node
					queue.enqueue(node.right, level + 1);
				}
				if (level >= a && level <= b)
				{
					status = true;
					print("  " + node.data);
				}
				//remove element into queue
				queue.dequeue();
			}
			if (status == false)
			{
				print(" None\n");
			}
		}
	}
}
object Main
{
	def main(args: Array[String]): Unit = {
		//Object of Binary Tree
		var tree: BinaryTree = new BinaryTree();
		/*  
				Construct Binary Tree
				-----------------------
				       10
				     /   \
				    2     3
				   /     / \
				  4     9   5
				 /  \    \    \
				7    3    6   20
				    /  \     /
				   2    8   -3
				         \    
				          9
				-----------------------
				*/
		//Add node
		tree.root = new TreeNode(10);
		tree.root.left = new TreeNode(2);
		tree.root.right = new TreeNode(3);
		tree.root.right.right = new TreeNode(5);
		tree.root.right.left = new TreeNode(9);
		tree.root.left.left = new TreeNode(4);
		tree.root.left.left.left = new TreeNode(7);
		tree.root.left.left.right = new TreeNode(3);
		tree.root.right.left.right = new TreeNode(6);
		tree.root.right.right.right = new TreeNode(20);
		tree.root.right.right.right.left = new TreeNode(-3);
		tree.root.left.left.right.left = new TreeNode(2);
		tree.root.left.left.right.right = new TreeNode(8);
		tree.root.left.left.right.right.right = new TreeNode(9);
		tree.print_level_nodes(2, 4);
		tree.print_level_nodes(4, 6);
		tree.print_level_nodes(1, 3);
		tree.print_level_nodes(7, 8);
	}
}

Output

 Node between level (2-4) is
  2  3  4  9  5  7  3  6  20
 Node between level (4-6) is
  7  3  6  20  2  8  -3  9
 Node between level (1-3) is
  10  2  3  4  9  5
 Node between level (7-8) is
 None
/* 
  Swift 4 program 
  Print all palindromic levels of a binary tree
*/
//Binary Tree node
class TreeNode
{
	var data: Int;
	var left: TreeNode? ;
	var right: TreeNode? ;
	init(_ data: Int)
	{
		//set node value
		self.data = data;
		self.left = nil;
		self.right = nil;
	}
}
// Queue Node
class QueueNode
{
	var element: TreeNode? ;
	var next: QueueNode? ;
	var level: Int;
	init(_ element: TreeNode? , _ level : Int)
	{
		self.element = element;
		self.next = nil;
		self.level = level;
	}
}
//Define custom queue class
class MyQueue
{
	var front: QueueNode? ;
	var tail: QueueNode? ;
	init()
	{
		self.front = nil;
		self.tail = nil;
	}
	//Add a new node at last of queue
	func enqueue(_ element: TreeNode? , _ level : Int)
	{
		let new_node: QueueNode? = QueueNode(element, level);
		if (self.front == nil)
		{
			//When first node of queue
			self.front = new_node;
		}
		else
		{
			//Add node at last position
			self.tail!.next = new_node;
		}
		self.tail = new_node;
	}
	//Delete first node of queue
	func dequeue()
	{
		if (self.front != nil)
		{
			if (self.tail === self.front)
			{
				self.tail = nil;
				self.front = nil;
			}
			else
			{
				self.front = self.front!.next;
			}
		}
	}
	func is_empty() -> Bool
	{
		if (self.front == nil)
		{
			return true;
		}
		else
		{
			return false;
		}
	}
}
class BinaryTree
{
	var root: TreeNode? ;
	init()
	{
		// Set initial tree root to null
		self.root = nil;
	}
	// This are printing all binary tree nodes, between given (A to B) levels
	func print_level_nodes(_ a: Int, _ b: Int)
	{
		if (self.root == nil)
		{
			print("\n Empty Binary Tree \n", terminator: "");
		}
		else
		{
			//Get top node in tree
			var node: TreeNode? = self.root;
			var level: Int = 1;
			//Create a Queue
			let queue: MyQueue = MyQueue();
			//Add first node at the level of one
			queue.enqueue(node, level);
			print("\n Node between level (", a ,"-", b ,") is \n", terminator: "");
			// Result indicator
			var status: Bool = false;
			//Execute loop until the queue is not empty
			while (queue.is_empty() == false)
			{
				node = queue.front!.element;
				level = queue.front!.level;
				if (node!.left != nil)
				{
					//Add left node
					queue.enqueue(node!.left, level + 1);
				}
				if (node!.right != nil)
				{
					//Add right node
					queue.enqueue(node!.right, level + 1);
				}
				if (level >= a && level <= b)
				{
					status = true;
					print("  ", node!.data, terminator: "");
				}
				//remove element into queue
				queue.dequeue();
			}
			if (status == false)
			{
				print(" None\n", terminator: "");
			}
		}
	}
}
func main()
{
	//Object of Binary Tree
	let tree: BinaryTree = BinaryTree();
	tree.root = TreeNode(10);
	tree.root!.left = TreeNode(2);
	tree.root!.right = TreeNode(3);
	tree.root!.right!.right = TreeNode(5);
	tree.root!.right!.left = TreeNode(9);
	tree.root!.left!.left = TreeNode(4);
	tree.root!.left!.left!.left = TreeNode(7);
	tree.root!.left!.left!.right = TreeNode(3);
	tree.root!.right!.left!.right = TreeNode(6);
	tree.root!.right!.right!.right = TreeNode(20);
	tree.root!.right!.right!.right!.left = TreeNode(-3);
	tree.root!.left!.left!.right!.left = TreeNode(2);
	tree.root!.left!.left!.right!.right = TreeNode(8);
	tree.root!.left!.left!.right!.right!.right = TreeNode(9);
	tree.print_level_nodes(2, 4);
	tree.print_level_nodes(4, 6);
	tree.print_level_nodes(1, 3);
	tree.print_level_nodes(7, 8);
}
main();

Output

 Node between level ( 2 - 4 ) is
   2   3   4   9   5   7   3   6   20
 Node between level ( 4 - 6 ) is
   7   3   6   20   2   8   -3   9
 Node between level ( 1 - 3 ) is
   10   2   3   4   9   5
 Node between level ( 7 - 8 ) is
 None

Algorithm

  1. Define the TreeNode class to represent a node in the binary tree. Each node will have a data value and pointers to its left and right children.
  2. Define the QueueNode class to represent a node in the custom queue. Each node will contain a pointer to a binary tree node, its level, and a link to the next node in the queue.
  3. Define the MyQueue class to implement the custom queue. It will have methods to enqueue and dequeue nodes, as well as a method to check if the queue is empty.
  4. Define the BinaryTree class to represent the binary tree. It will have a method print_level_nodes(int a, int b) to print all the nodes between levels a and b.
  5. Perform a level order traversal of the binary tree using a queue. For each level, check if it falls between the given levels a and b (inclusive). If it does, print the nodes; otherwise, skip that level.

Time Complexity

  • The time complexity of performing a level order traversal of the binary tree to find nodes between two levels is O(N), where N is the number of nodes in the tree.
  • Therefore, the overall time complexity of the algorithm is O(N), where N is the number of nodes in the binary tree.




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