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# Print the middle nodes of each level of a binary tree

The problem at hand involves printing the middle nodes of each level in a binary tree. The middle node of a level is the node that is located in the center of that level when traversed from left to right. The task is to print these middle nodes for each level in the tree.

## Problem Statement

Given a binary tree, the goal is to print the middle nodes of each level in separate lines.

## Example

Consider the following binary tree:

``````
-6
/   \
4    -7
/ \     \
2   3     12
/ \   /  \
10 -4 5    9
/     \      \
1       7      8``````

The output for this tree would be:

``````-6
4 -7
3
-4 5
7``````

Note more than 2 middle node when levels are number of nodes are even number of counting.

## Idea to Solve

To solve this problem, we can perform a level order traversal of the tree using two queues. One queue is used to store the nodes of the current level, and the other queue is used to store the nodes of the next level. While traversing each level, we extract the middle node from the current level's queue and print it.

## Pseudocode

``````middleLevelNode():
if root is null:
return

Create two empty queues, q1 and q2
Create an empty ArrayList called record
Set level = 1

Enqueue the root into q1

while q1 is not empty or q2 is not empty:
while q1 is not empty:
Dequeue a node from q1
Enqueue its left and right children into q2

Print the middle node from record
Clear the record
Increment level

while q2 is not empty:
Dequeue a node from q2
Enqueue its left and right children into q1

Print the middle node from record
Clear the record
Increment level``````

## Algorithm Explanation

1. We start by initializing two queues, q1 and q2, and an empty ArrayList called record. We also initialize the level counter to 1.
2. We enqueue the root node into q1 to start the level order traversal.
3. During each iteration, we extract nodes from q1 while enqueueing their left and right children into q2. We also add the data of these nodes to the record.
4. After processing the nodes in q1, we calculate the middle index in the record and print the middle node's data. We then clear the record and increment the level.
5. We repeat the same process with q2, enqueuing nodes into q1, adding data to the record, calculating the middle node, and printing it.
6. This process continues until both q1 and q2 are empty.

## Code Solution

``````import java.util.ArrayList;
// Java program for
// Print the middle nodes of each level 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 QNode
{
public TreeNode n;
public QNode next;
public QNode(TreeNode n)
{
this.n = n;
this.next = null;
}
}
//Define custom queue class
class MyQueue
{
public QNode front;
public QNode rear;
public int size;
public MyQueue()
{
this.front = null;
this.rear = null;
this.size = 0;
}
// Add a new node at last of queue
public void enqueue(TreeNode n)
{
QNode node = new QNode(n);
if (this.front == null)
{
// When first node of queue
this.front = node;
}
else
{
// Add node at last level
this.rear.next = node;
}
this.size++;
this.rear = node;
}
// Delete front node of queue
public void dequeue()
{
if (this.front != null)
{
if (this.rear == this.front)
{
this.rear = null;
this.front = null;
}
else
{
this.front = this.front.next;
}
this.size--;
}
}
public int isSize()
{
return this.size;
}
public boolean isEmpty()
{
if (this.isSize() == 0)
{
return true;
}
return false;
}
public TreeNode peek()
{
if (this.isSize() == 0)
{
return null;
}
else
{
return this.front.n;
}
}
}
// Define Binary Tree
public class BinaryTree
{
public TreeNode root;
public BinaryTree()
{
this.root = null;
}
// Print the middle element of given level
public void printMiddleNode(ArrayList < Integer > level)
{
if (level.size() > 0)
{
int middle = level.size() / 2;
if ((level.size() % 2) == 0)
{
// When two middle element possible
System.out.print("\n " + level.get(middle - 1));
System.out.print(" " + level.get(middle));
}
else
{
System.out.print("\n " + level.get(middle));
}
}
}
// This is display middle node of each level in binary tree
public void middleLevelNode()
{
if (this.root == null)
{
// When tree is empty
return;
}
// Auxiliary queue which is capable to contain a tree level nodes
MyQueue q1 = new MyQueue();
MyQueue q2 = new MyQueue();
// Auxiliary temp variable
TreeNode temp = null;
int level = 1;
// It will be use assemble a level node.
ArrayList < Integer > record = new ArrayList < Integer > ();
// Add first node in q1
q1.enqueue(this.root);
// This loop execute until auxiliary queue q1 and q2 are not empty
while (!q1.isEmpty() || !q2.isEmpty())
{
// Execute loop until q1 queue are not empty
// And store the next level node in q2 queue
while (!q1.isEmpty())
{
// Get top node of q1 queue
temp = q1.peek();
if (temp.left != null)
{
q2.enqueue(temp.left);
}
if (temp.right != null)
{
q2.enqueue(temp.right);
}
// Remove top element of q1 queue
q1.dequeue();
}
printMiddleNode(record);
record.clear();
level++;
// Execute loop until q2 queue are not empty
// And store the next level node in q1 queue
while (!q2.isEmpty())
{
// Get top node of q2 queue
temp = q2.peek();
if (temp.left != null)
{
q1.enqueue(temp.left);
}
if (temp.right != null)
{
q1.enqueue(temp.right);
}
// Remove top element of q2 queue
q2.dequeue();
}
printMiddleNode(record);
record.clear();
level++;
}
}
public static void main(String[] args)
{
BinaryTree tree = new BinaryTree();
/*
Create Binary Tree
-----------------
-6
/   \
4    -7
/ \     \
2   3     12
/ \   /  \
10 -4 5    9
/     \      \
1      7      8

*/
tree.root = new TreeNode(-6);
tree.root.left = new TreeNode(4);
tree.root.left.right = new TreeNode(3);
tree.root.left.right.left = new TreeNode(10);
tree.root.left.right.left.left = new TreeNode(1);
tree.root.left.right.right = new TreeNode(-4);
tree.root.left.right.right.right = new TreeNode(7);
tree.root.left.left = new TreeNode(2);
tree.root.right = new TreeNode(-7);
tree.root.right.right = new TreeNode(12);
tree.root.right.right.left = new TreeNode(5);
tree.root.right.right.right = new TreeNode(9);
tree.root.right.right.right.right = new TreeNode(8);
tree.middleLevelNode();
}
}``````

#### input

`````` -6
4 -7
3
-4 5
7``````
``````// Include header file
#include <iostream>
#include <vector>
using namespace std;

// C++ program for
// Print the middle nodes of each level 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 QNode
{
public:
TreeNode *n;
QNode *next;
QNode(TreeNode *n)
{
this->n = n;
this->next = NULL;
}
};
//Define custom queue class
class MyQueue
{
public:
QNode *front;
QNode *rear;
int size;
MyQueue()
{
this->front = NULL;
this->rear = NULL;
this->size = 0;
}
// Add a new node at last of queue
void enqueue(TreeNode *n)
{
QNode *node = new QNode(n);
if (this->front == NULL)
{
// When first node of queue
this->front = node;
}
else
{
// Add node at last level
this->rear->next = node;
}
this->size++;
this->rear = node;
}
// Delete front node of queue
void dequeue()
{

if (this->front != NULL)
{
QNode *temp = this->front;
if (this->rear == this->front)
{
this->rear = NULL;
this->front = NULL;
}
else
{
this->front = this->front->next;
}
this->size--;
// Free memory
delete temp;
}
}
int isSize()
{
return this->size;
}
bool isEmpty()
{
if (this->isSize() == 0)
{
return true;
}
return false;
}
TreeNode *peek()
{
if (this->isSize() == 0)
{
return NULL;
}
else
{
return this->front->n;
}
}
};
// Define Binary Tree
class BinaryTree
{
public: TreeNode *root;
BinaryTree()
{
this->root = NULL;
}
// Print the middle element of given level
void printMiddleNode(vector < int > level)
{
if (level.size() > 0)
{
int middle = level.size() / 2;
if ((level.size() % 2) == 0)
{
// When two middle element possible
cout << "\n " << level.at(middle - 1);
cout << " " << level.at(middle);
}
else
{
cout << "\n " << level.at(middle);
}
}
}
// This is display middle node of each level in binary tree
void middleLevelNode()
{
if (this->root == NULL)
{
// When tree is empty
return;
}
// Auxiliary queue which is capable to contain a tree level nodes
MyQueue *q1 = new MyQueue();
MyQueue *q2 = new MyQueue();
// Auxiliary temp variable
TreeNode *temp = NULL;
int level = 1;
// It will be use assemble a level node.
vector < int > record ;
// Add first node in q1
q1->enqueue(this->root);
// This loop execute until auxiliary queue q1 and q2 are not empty
while (!q1->isEmpty() || !q2->isEmpty())
{
// Execute loop until q1 queue are not empty
// And store the next level node in q2 queue
while (!q1->isEmpty())
{
// Get top node of q1 queue
temp = q1->peek();
record.push_back(temp->data);
if (temp->left != NULL)
{
q2->enqueue(temp->left);
}
if (temp->right != NULL)
{
q2->enqueue(temp->right);
}
// Remove top element of q1 queue
q1->dequeue();
}
this->printMiddleNode(record);
record.clear();
level++;
// Execute loop until q2 queue are not empty
// And store the next level node in q1 queue
while (!q2->isEmpty())
{
// Get top node of q2 queue
temp = q2->peek();
record.push_back(temp->data);
if (temp->left != NULL)
{
q1->enqueue(temp->left);
}
if (temp->right != NULL)
{
q1->enqueue(temp->right);
}
// Remove top element of q2 queue
q2->dequeue();
}
this->printMiddleNode(record);
record.clear();
level++;
}
}
};
int main()
{
BinaryTree *tree = new BinaryTree();
/*
Create Binary Tree
-----------------
-6
/   \
4    -7
/ \     \
2   3     12
/ \   /  \
10 -4 5    9
/     \      \
1      7      8
*/
tree->root = new TreeNode(-6);
tree->root->left = new TreeNode(4);
tree->root->left->right = new TreeNode(3);
tree->root->left->right->left = new TreeNode(10);
tree->root->left->right->left->left = new TreeNode(1);
tree->root->left->right->right = new TreeNode(-4);
tree->root->left->right->right->right = new TreeNode(7);
tree->root->left->left = new TreeNode(2);
tree->root->right = new TreeNode(-7);
tree->root->right->right = new TreeNode(12);
tree->root->right->right->left = new TreeNode(5);
tree->root->right->right->right = new TreeNode(9);
tree->root->right->right->right->right = new TreeNode(8);
tree->middleLevelNode();
return 0;
}``````

#### input

`````` -6
4 -7
3
-4 5
7``````
``````// Include namespace system
using System;
using System.Collections.Generic;
// Csharp program for
// Print the middle nodes of each level of a binary tree

// Binary Tree node
public 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
public class QNode
{
public TreeNode n;
public QNode next;
public QNode(TreeNode n)
{
this.n = n;
this.next = null;
}
}
//Define custom queue class
public class MyQueue
{
public QNode front;
public QNode rear;
public int size;
public MyQueue()
{
this.front = null;
this.rear = null;
this.size = 0;
}
// Add a new node at last of queue
public void enqueue(TreeNode n)
{
QNode node = new QNode(n);
if (this.front == null)
{
// When first node of queue
this.front = node;
}
else
{
// Add node at last level
this.rear.next = node;
}
this.size++;
this.rear = node;
}
// Delete front node of queue
public void dequeue()
{
if (this.front != null)
{
if (this.rear == this.front)
{
this.rear = null;
this.front = null;
}
else
{
this.front = this.front.next;
}
this.size--;
}
}
public int isSize()
{
return this.size;
}
public Boolean isEmpty()
{
if (this.isSize() == 0)
{
return true;
}
return false;
}
public TreeNode peek()
{
if (this.isSize() == 0)
{
return null;
}
else
{
return this.front.n;
}
}
}
// Define Binary Tree
public class BinaryTree
{
public TreeNode root;
public BinaryTree()
{
this.root = null;
}
// Print the middle element of given level
public void printMiddleNode(List<int> level)
{
if (level.Count > 0)
{
int middle = level.Count / 2;
if ((level.Count % 2) == 0)
{
// When two middle element possible
Console.Write("\n " + level[middle - 1]);
Console.Write(" " + level[middle]);
}
else
{
Console.Write("\n " + level[middle]);
}
}
}
// This is display middle node of each level in binary tree
public void middleLevelNode()
{
if (this.root == null)
{
// When tree is empty
return;
}
// Auxiliary queue which is capable to contain a tree level nodes
MyQueue q1 = new MyQueue();
MyQueue q2 = new MyQueue();
// Auxiliary temp variable
TreeNode temp = null;
int level = 1;
// It will be use assemble a level node.
List < int > record = new List < int > ();
// Add first node in q1
q1.enqueue(this.root);
// This loop execute until auxiliary queue q1 and q2 are not empty
while (!q1.isEmpty() || !q2.isEmpty())
{
// Execute loop until q1 queue are not empty
// And store the next level node in q2 queue
while (!q1.isEmpty())
{
// Get top node of q1 queue
temp = q1.peek();
if (temp.left != null)
{
q2.enqueue(temp.left);
}
if (temp.right != null)
{
q2.enqueue(temp.right);
}
// Remove top element of q1 queue
q1.dequeue();
}
this.printMiddleNode(record);
record.Clear();
level++;
// Execute loop until q2 queue are not empty
// And store the next level node in q1 queue
while (!q2.isEmpty())
{
// Get top node of q2 queue
temp = q2.peek();
if (temp.left != null)
{
q1.enqueue(temp.left);
}
if (temp.right != null)
{
q1.enqueue(temp.right);
}
// Remove top element of q2 queue
q2.dequeue();
}
this.printMiddleNode(record);
record.Clear();
level++;
}
}
public static void Main(String[] args)
{
BinaryTree tree = new BinaryTree();
/*
Create Binary Tree
-----------------
-6
/   \
4    -7
/ \     \
2   3     12
/ \   /  \
10 -4 5    9
/     \      \
1      7      8
*/
tree.root = new TreeNode(-6);
tree.root.left = new TreeNode(4);
tree.root.left.right = new TreeNode(3);
tree.root.left.right.left = new TreeNode(10);
tree.root.left.right.left.left = new TreeNode(1);
tree.root.left.right.right = new TreeNode(-4);
tree.root.left.right.right.right = new TreeNode(7);
tree.root.left.left = new TreeNode(2);
tree.root.right = new TreeNode(-7);
tree.root.right.right = new TreeNode(12);
tree.root.right.right.left = new TreeNode(5);
tree.root.right.right.right = new TreeNode(9);
tree.root.right.right.right.right = new TreeNode(8);
tree.middleLevelNode();
}
}``````

#### input

`````` -6
4 -7
3
-4 5
7``````
``````<?php
// Php program for
// Print the middle nodes of each level of a binary tree

// Binary Tree node
class TreeNode
{
public \$data;
public \$left;
public \$right;
public	function __construct(\$data)
{
// Set node value
\$this->data = \$data;
\$this->left = NULL;
\$this->right = NULL;
}
}
// Queue Node
class QNode
{
public \$n;
public \$next;
public	function __construct(\$n)
{
\$this->n = \$n;
\$this->next = NULL;
}
}
//Define custom queue class
class MyQueue
{
public \$front;
public \$rear;
public \$size;
public	function __construct()
{
\$this->front = NULL;
\$this->rear = NULL;
\$this->size = 0;
}
// Add a new node at last of queue
public	function enqueue(\$n)
{
\$node = new QNode(\$n);
if (\$this->front == NULL)
{
// When first node of queue
\$this->front = \$node;
}
else
{
// Add node at last level
\$this->rear->next = \$node;
}
\$this->size++;
\$this->rear = \$node;
}
// Delete front node of queue
public	function dequeue()
{
if (\$this->front != NULL)
{
if (\$this->rear == \$this->front)
{
\$this->rear = NULL;
\$this->front = NULL;
}
else
{
\$this->front = \$this->front->next;
}
\$this->size--;
}
}
public	function isSize()
{
return \$this->size;
}
public	function isEmpty()
{
if (\$this->isSize() == 0)
{
return true;
}
return false;
}
public	function peek()
{
if (\$this->isSize() == 0)
{
return NULL;
}
else
{
return \$this->front->n;
}
}
}
// Define Binary Tree
class BinaryTree
{
public \$root;
public	function __construct()
{
\$this->root = NULL;
}
// Print the middle element of given level
public	function printMiddleNode(\$level)
{
if (count(\$level) > 0)
{
\$middle = (int)(count(\$level) / 2);
if ((count(\$level) % 2) == 0)
{
// When two middle element possible
echo("\n ".\$level[\$middle - 1]);
echo(" ".\$level[\$middle]);
}
else
{
echo("\n ".\$level[\$middle]);
}
}
}
// This is display middle node of each level in binary tree
public	function middleLevelNode()
{
if (\$this->root == NULL)
{
// When tree is empty
return;
}
// Auxiliary queue which is capable to contain a tree level nodes
\$q1 = new MyQueue();
\$q2 = new MyQueue();
// Auxiliary temp variable
\$temp = NULL;
\$level = 1;
// It will be use assemble a level node.
\$record =  array();
// Add first node in q1
\$q1->enqueue(\$this->root);
// This loop execute until auxiliary queue q1 and q2 are not empty
while (!\$q1->isEmpty() || !\$q2->isEmpty())
{
// Execute loop until q1 queue are not empty
// And store the next level node in q2 queue
while (!\$q1->isEmpty())
{
// Get top node of q1 queue
\$temp = \$q1->peek();
\$record[] = \$temp->data;
if (\$temp->left != NULL)
{
\$q2->enqueue(\$temp->left);
}
if (\$temp->right != NULL)
{
\$q2->enqueue(\$temp->right);
}
// Remove top element of q1 queue
\$q1->dequeue();
}
\$this->printMiddleNode(\$record);
\$record = array();
\$level++;
// Execute loop until q2 queue are not empty
// And store the next level node in q1 queue
while (!\$q2->isEmpty())
{
// Get top node of q2 queue
\$temp = \$q2->peek();
\$record[] = \$temp->data;
if (\$temp->left != NULL)
{
\$q1->enqueue(\$temp->left);
}
if (\$temp->right != NULL)
{
\$q1->enqueue(\$temp->right);
}
// Remove top element of q2 queue
\$q2->dequeue();
}
\$this->printMiddleNode(\$record);
\$record = array();
\$level++;
}
}
}

function main()
{
\$tree = new BinaryTree();
/*
Create Binary Tree
-----------------
-6
/   \
4    -7
/ \     \
2   3     12
/ \   /  \
10 -4 5    9
/     \      \
1      7      8
*/
\$tree->root = new TreeNode(-6);
\$tree->root->left = new TreeNode(4);
\$tree->root->left->right = new TreeNode(3);
\$tree->root->left->right->left = new TreeNode(10);
\$tree->root->left->right->left->left = new TreeNode(1);
\$tree->root->left->right->right = new TreeNode(-4);
\$tree->root->left->right->right->right = new TreeNode(7);
\$tree->root->left->left = new TreeNode(2);
\$tree->root->right = new TreeNode(-7);
\$tree->root->right->right = new TreeNode(12);
\$tree->root->right->right->left = new TreeNode(5);
\$tree->root->right->right->right = new TreeNode(9);
\$tree->root->right->right->right->right = new TreeNode(8);
\$tree->middleLevelNode();
}
main();``````

#### input

`````` -6
4 -7
3
-4 5
7``````
``````// Node JS program for
// Print the middle nodes of each level 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 QNode
{
constructor(n)
{
this.n = n;
this.next = null;
}
}
//Define custom queue class
class MyQueue
{
constructor()
{
this.front = null;
this.rear = null;
this.size = 0;
}
// Add a new node at last of queue
enqueue(n)
{
var node = new QNode(n);
if (this.front == null)
{
// When first node of queue
this.front = node;
}
else
{
// Add node at last level
this.rear.next = node;
}
this.size++;
this.rear = node;
}
// Delete front node of queue
dequeue()
{
if (this.front != null)
{
if (this.rear == this.front)
{
this.rear = null;
this.front = null;
}
else
{
this.front = this.front.next;
}
this.size--;
}
}
isSize()
{
return this.size;
}
isEmpty()
{
if (this.isSize() == 0)
{
return true;
}
return false;
}
peek()
{
if (this.isSize() == 0)
{
return null;
}
else
{
return this.front.n;
}
}
}
// Define Binary Tree
class BinaryTree
{
constructor()
{
this.root = null;
}
// Print the middle element of given level
printMiddleNode(level)
{
if (level.length > 0)
{
var middle = parseInt(level.length / 2);
if ((level.length % 2) == 0)
{
// When two middle element possible
process.stdout.write("\n " + level[middle - 1]);
process.stdout.write(" " + level[middle]);
}
else
{
process.stdout.write("\n " + level[middle]);
}
}
}
// This is display middle node of each level in binary tree
middleLevelNode()
{
if (this.root == null)
{
// When tree is empty
return;
}
// Auxiliary queue which is capable to contain a tree level nodes
var q1 = new MyQueue();
var q2 = new MyQueue();
// Auxiliary temp variable
var temp = null;
var level = 1;
// It will be use assemble a level node.
var record = [];
// Add first node in q1
q1.enqueue(this.root);
// This loop execute until auxiliary queue q1 and q2 are not empty
while (!q1.isEmpty() || !q2.isEmpty())
{
// Execute loop until q1 queue are not empty
// And store the next level node in q2 queue
while (!q1.isEmpty())
{
// Get top node of q1 queue
temp = q1.peek();
record.push(temp.data);
if (temp.left != null)
{
q2.enqueue(temp.left);
}
if (temp.right != null)
{
q2.enqueue(temp.right);
}
// Remove top element of q1 queue
q1.dequeue();
}
this.printMiddleNode(record);
record = [];
level++;
// Execute loop until q2 queue are not empty
// And store the next level node in q1 queue
while (!q2.isEmpty())
{
// Get top node of q2 queue
temp = q2.peek();
record.push(temp.data);
if (temp.left != null)
{
q1.enqueue(temp.left);
}
if (temp.right != null)
{
q1.enqueue(temp.right);
}
// Remove top element of q2 queue
q2.dequeue();
}
this.printMiddleNode(record);
record = [];
level++;
}
}
}

function main()
{
var tree = new BinaryTree();
/*
Create Binary Tree
-----------------
-6
/   \
4    -7
/ \     \
2   3     12
/ \   /  \
10 -4 5    9
/     \      \
1      7      8
*/
tree.root = new TreeNode(-6);
tree.root.left = new TreeNode(4);
tree.root.left.right = new TreeNode(3);
tree.root.left.right.left = new TreeNode(10);
tree.root.left.right.left.left = new TreeNode(1);
tree.root.left.right.right = new TreeNode(-4);
tree.root.left.right.right.right = new TreeNode(7);
tree.root.left.left = new TreeNode(2);
tree.root.right = new TreeNode(-7);
tree.root.right.right = new TreeNode(12);
tree.root.right.right.left = new TreeNode(5);
tree.root.right.right.right = new TreeNode(9);
tree.root.right.right.right.right = new TreeNode(8);
tree.middleLevelNode();
}
main();``````

#### input

`````` -6
4 -7
3
-4 5
7``````
``````#  Python 3 program for
#  Print the middle nodes of each level 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 QNode :
def __init__(self, n) :
self.n = n
self.next = None

# Define custom queue class
class MyQueue :
def __init__(self) :
self.front = None
self.rear = None
self.size = 0

#  Add a new node at last of queue
def enqueue(self, n) :
node = QNode(n)
if (self.front == None) :
#  When first node of queue
self.front = node
else :
#  Add node at last level
self.rear.next = node

self.size += 1
self.rear = node

#  Delete front node of queue
def dequeue(self) :
if (self.front != None) :
if (self.rear == self.front) :
self.rear = None
self.front = None
else :
self.front = self.front.next

self.size -= 1

def isSize(self) :
return self.size

def isEmpty(self) :
if (self.isSize() == 0) :
return True

return False

def peek(self) :
if (self.isSize() == 0) :
return None
else :
return self.front.n

#  Define Binary Tree
class BinaryTree :
def __init__(self) :
self.root = None

#  Print the middle element of given level
def printMiddleNode(self, level) :
if (len(level) > 0) :
middle = int(len(level) / 2)
if ((len(level) % 2) == 0) :
#  When two middle element possible
print("\n ", level[middle - 1], end = "")
print(" ", level[middle], end = "")
else :
print("\n ", level[middle], end = "")

#  This is display middle node of each level in binary tree
def middleLevelNode(self) :
if (self.root == None) :
#  When tree is empty
return

#  Auxiliary queue which is capable to contain a tree level nodes
q1 = MyQueue()
q2 = MyQueue()
#  Auxiliary temp variable
temp = None
level = 1
#  It will be use assemble a level node.
record = []
#  Add first node in q1
q1.enqueue(self.root)
#  This loop execute until auxiliary queue q1 and q2 are not empty
while (not q1.isEmpty() or not q2.isEmpty()) :
#  Execute loop until q1 queue are not empty
#  And store the next level node in q2 queue
while (not q1.isEmpty()) :
#  Get top node of q1 queue
temp = q1.peek()
record.append(temp.data)
if (temp.left != None) :
q2.enqueue(temp.left)

if (temp.right != None) :
q2.enqueue(temp.right)

#  Remove top element of q1 queue
q1.dequeue()

self.printMiddleNode(record)
record.clear()
level += 1
#  Execute loop until q2 queue are not empty
#  And store the next level node in q1 queue
while (not q2.isEmpty()) :
#  Get top node of q2 queue
temp = q2.peek()
record.append(temp.data)
if (temp.left != None) :
q1.enqueue(temp.left)

if (temp.right != None) :
q1.enqueue(temp.right)

#  Remove top element of q2 queue
q2.dequeue()

self.printMiddleNode(record)
record.clear()
level += 1

def main() :
tree = BinaryTree()
#    Create Binary Tree
#    -----------------
#         -6
#       /   \
#      4    -7
#     / \     \
#    2   3     12
#       / \   /  \
#      10 -4 5    9
#     /     \      \
#    1      7      8
tree.root = TreeNode(-6)
tree.root.left = TreeNode(4)
tree.root.left.right = TreeNode(3)
tree.root.left.right.left = TreeNode(10)
tree.root.left.right.left.left = TreeNode(1)
tree.root.left.right.right = TreeNode(-4)
tree.root.left.right.right.right = TreeNode(7)
tree.root.left.left = TreeNode(2)
tree.root.right = TreeNode(-7)
tree.root.right.right = TreeNode(12)
tree.root.right.right.left = TreeNode(5)
tree.root.right.right.right = TreeNode(9)
tree.root.right.right.right.right = TreeNode(8)
tree.middleLevelNode()

if __name__ == "__main__": main()``````

#### input

``````  -6
4  -7
3
-4  5
7``````
``````#  Ruby program for
#  Print the middle nodes of each level of a binary tree

#  Binary Tree node
class TreeNode
# Define the accessor and reader of class TreeNode
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 QNode
# Define the accessor and reader of class QNode
attr_accessor :n, :next
def initialize(n)
self.n = n
self.next = nil
end

end

# Define custom queue class
class MyQueue
# Define the accessor and reader of class MyQueue
attr_accessor :front, :rear, :size
def initialize()
self.front = nil
self.rear = nil
self.size = 0
end

#  Add a new node at last of queue
def enqueue(n)
node = QNode.new(n)
if (self.front == nil)
#  When first node of queue
self.front = node
else
#  Add node at last level
self.rear.next = node
end

self.size += 1
self.rear = node
end

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

self.size -= 1
end

end

def isSize()
return self.size
end

def isEmpty()
if (self.isSize() == 0)
return true
end

return false
end

def peek()
if (self.isSize() == 0)
return nil
else
return self.front.n
end

end

end

#  Define Binary Tree
class BinaryTree
# Define the accessor and reader of class BinaryTree
attr_accessor :root
def initialize()
self.root = nil
end

#  Print the middle element of given level
def printMiddleNode(level)
if (level.length > 0)
middle = level.length / 2
if ((level.length % 2) == 0)
#  When two middle element possible
print("\n ", level[middle - 1])
print(" ", level[middle])
else
print("\n ", level[middle])
end

end

end

#  This is display middle node of each level in binary tree
def middleLevelNode()
if (self.root == nil)
#  When tree is empty
return
end

#  Auxiliary queue which is capable to contain a tree level nodes
q1 = MyQueue.new()
q2 = MyQueue.new()
#  Auxiliary temp variable
temp = nil
level = 1
#  It will be use assemble a level node.
record = []
#  Add first node in q1
q1.enqueue(self.root)
#  This loop execute until auxiliary queue q1 and q2 are not empty
while (!q1.isEmpty() || !q2.isEmpty())
#  Execute loop until q1 queue are not empty
#  And store the next level node in q2 queue
while (!q1.isEmpty())
#  Get top node of q1 queue
temp = q1.peek()
record.push(temp.data)
if (temp.left != nil)
q2.enqueue(temp.left)
end

if (temp.right != nil)
q2.enqueue(temp.right)
end

#  Remove top element of q1 queue
q1.dequeue()
end

self.printMiddleNode(record)
record.clear()
level += 1
#  Execute loop until q2 queue are not empty
#  And store the next level node in q1 queue
while (!q2.isEmpty())
#  Get top node of q2 queue
temp = q2.peek()
record.push(temp.data)
if (temp.left != nil)
q1.enqueue(temp.left)
end

if (temp.right != nil)
q1.enqueue(temp.right)
end

#  Remove top element of q2 queue
q2.dequeue()
end

self.printMiddleNode(record)
record.clear()
level += 1
end

end

end

def main()
tree = BinaryTree.new()
#    Create Binary Tree
#    -----------------
#         -6
#       /   \
#      4    -7
#     / \     \
#    2   3     12
#       / \   /  \
#      10 -4 5    9
#     /     \      \
#    1      7      8
tree.root = TreeNode.new(-6)
tree.root.left = TreeNode.new(4)
tree.root.left.right = TreeNode.new(3)
tree.root.left.right.left = TreeNode.new(10)
tree.root.left.right.left.left = TreeNode.new(1)
tree.root.left.right.right = TreeNode.new(-4)
tree.root.left.right.right.right = TreeNode.new(7)
tree.root.left.left = TreeNode.new(2)
tree.root.right = TreeNode.new(-7)
tree.root.right.right = TreeNode.new(12)
tree.root.right.right.left = TreeNode.new(5)
tree.root.right.right.right = TreeNode.new(9)
tree.root.right.right.right.right = TreeNode.new(8)
tree.middleLevelNode()
end

main()``````

#### input

`````` -6
4 -7
3
-4 5
7``````
``````import scala.collection.mutable._;
// Scala program for
// Print the middle nodes of each level of a binary tree

// Binary Tree node
class TreeNode(var data: Int , var left: TreeNode , var right: TreeNode)
{
def this(data: Int)
{
// Set node value
this(data,null,null);
}
}
// Queue Node
class QNode(var n: TreeNode , var next: QNode)
{
def this(n: TreeNode)
{
this(n,null);
}
}
//Define custom queue class
class MyQueue(var front: QNode , var rear: QNode , var size: Int)
{
def this()
{
this(null, null,0);
}
// Add a new node at last of queue
def enqueue(n: TreeNode): Unit = {
var node: QNode = new QNode(n);
if (this.front == null)
{
// When first node of queue
this.front = node;
}
else
{
// Add node at last level
this.rear.next = node;
}
this.size += 1;
this.rear = node;
}
// Delete front node of queue
def dequeue(): Unit = {
if (this.front != null)
{
if (this.rear == this.front)
{
this.rear = null;
this.front = null;
}
else
{
this.front = this.front.next;
}
this.size -= 1;
}
}
def isSize(): Int = {
return this.size;
}
def isEmpty(): Boolean = {
if (this.isSize() == 0)
{
return true;
}
return false;
}
def peek(): TreeNode = {
if (this.isSize() == 0)
{
return null;
}
else
{
return this.front.n;
}
}
}
// Define Binary Tree
class BinaryTree(var root: TreeNode)
{
def this()
{
this(null);
}
// Print the middle element of given level
def printMiddleNode(level: ArrayBuffer[Int]): Unit = {
if (level.size > 0)
{
var middle: Int = level.size / 2;
if ((level.size % 2) == 0)
{
// When two middle element possible
print("\n " + level(middle - 1));
print(" " + level(middle));
}
else
{
print("\n " + level(middle));
}
}
}
// This is display middle node of each level in binary tree
def middleLevelNode(): Unit = {
if (this.root == null)
{
// When tree is empty
return;
}
// Auxiliary queue which is capable to contain a tree level nodes
var q1: MyQueue = new MyQueue();
var q2: MyQueue = new MyQueue();
// Auxiliary temp variable
var temp: TreeNode = null;
var level: Int = 1;
// It will be use assemble a level node.
var record: ArrayBuffer[Int] = new ArrayBuffer[Int]();
// Add first node in q1
q1.enqueue(this.root);
// This loop execute until auxiliary queue q1 and q2 are not empty
while (!q1.isEmpty() || !q2.isEmpty())
{
// Execute loop until q1 queue are not empty
// And store the next level node in q2 queue
while (!q1.isEmpty())
{
// Get top node of q1 queue
temp = q1.peek();
record += temp.data;
if (temp.left != null)
{
q2.enqueue(temp.left);
}
if (temp.right != null)
{
q2.enqueue(temp.right);
}
// Remove top element of q1 queue
q1.dequeue();
}
printMiddleNode(record);
record.clear();
level += 1;
// Execute loop until q2 queue are not empty
// And store the next level node in q1 queue
while (!q2.isEmpty())
{
// Get top node of q2 queue
temp = q2.peek();
record += temp.data;
if (temp.left != null)
{
q1.enqueue(temp.left);
}
if (temp.right != null)
{
q1.enqueue(temp.right);
}
// Remove top element of q2 queue
q2.dequeue();
}
printMiddleNode(record);
record.clear();
level += 1;
}
}
}
object Main
{
def main(args: Array[String]): Unit = {
var tree: BinaryTree = new BinaryTree();
/*
Create Binary Tree
-----------------
-6
/   \
4    -7
/ \     \
2   3     12
/ \   /  \
10 -4 5    9
/     \      \
1      7      8
*/
tree.root = new TreeNode(-6);
tree.root.left = new TreeNode(4);
tree.root.left.right = new TreeNode(3);
tree.root.left.right.left = new TreeNode(10);
tree.root.left.right.left.left = new TreeNode(1);
tree.root.left.right.right = new TreeNode(-4);
tree.root.left.right.right.right = new TreeNode(7);
tree.root.left.left = new TreeNode(2);
tree.root.right = new TreeNode(-7);
tree.root.right.right = new TreeNode(12);
tree.root.right.right.left = new TreeNode(5);
tree.root.right.right.right = new TreeNode(9);
tree.root.right.right.right.right = new TreeNode(8);
tree.middleLevelNode();
}
}``````

#### input

`````` -6
4 -7
3
-4 5
7``````
``````// Swift 4 program for
// Print the middle nodes of each level 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 QNode
{
var n: TreeNode? ;
var next: QNode? ;
init(_ n: TreeNode? )
{
self.n = n;
self.next = nil;
}
}
//Define custom queue class
class MyQueue
{
var front: QNode? ;
var rear: QNode? ;
var size: Int;
init()
{
self.front = nil;
self.rear = nil;
self.size = 0;
}
// Add a new node at last of queue
func enqueue(_ n: TreeNode? )
{
let node: QNode = QNode(n);
if (self.front == nil)
{
// When first node of queue
self.front = node;
}
else
{
// Add node at last level
self.rear!.next = node;
}
self.size += 1;
self.rear = node;
}
// Delete front node of queue
func dequeue()
{
if (self.front  != nil)
{
if (self.rear === self.front)
{
self.rear = nil;
self.front = nil;
}
else
{
self.front = self.front!.next;
}
self.size -= 1;
}
}
func isSize()->Int
{
return self.size;
}
func isEmpty()->Bool
{
if (self.isSize() == 0)
{
return true;
}
return false;
}
func peek()->TreeNode?
{
if (self.isSize() == 0)
{
return nil;
}
else
{
return self.front!.n;
}
}
}
// Define Binary Tree
class BinaryTree
{
var root: TreeNode? ;
init()
{
self.root = nil;
}
// Print the middle element of given level
func printMiddleNode(_ level: [Int] )
{
if (level.count > 0)
{
let middle: Int = level.count / 2;
if ((level.count % 2) == 0)
{
// When two middle element possible
print("\n ", level[middle - 1], terminator: "");
print(" ", level[middle], terminator: "");
}
else
{
print("\n ", level[middle], terminator: "");
}
}
}
// This is display middle node of each level in binary tree
func middleLevelNode()
{
if (self.root == nil)
{
// When tree is empty
return;
}
// Auxiliary queue which is capable to contain a tree level nodes
let q1: MyQueue = MyQueue();
let q2: MyQueue = MyQueue();
// Auxiliary temp variable
var temp: TreeNode? = nil;
var level: Int = 1;
// It will be use assemble a level node.
var record: [Int] = [Int]();
// Add first node in q1
q1.enqueue(self.root);
// This loop execute until auxiliary queue q1 and q2 are not empty
while (!q1.isEmpty() || !q2.isEmpty())
{
// Execute loop until q1 queue are not empty
// And store the next level node in q2 queue
while (!q1.isEmpty())
{
// Get top node of q1 queue
temp = q1.peek();
record.append(temp!.data);
if (temp!.left  != nil)
{
q2.enqueue(temp!.left);
}
if (temp!.right  != nil)
{
q2.enqueue(temp!.right);
}
// Remove top element of q1 queue
q1.dequeue();
}
self.printMiddleNode(record);
record.removeAll();
level += 1;
// Execute loop until q2 queue are not empty
// And store the next level node in q1 queue
while (!q2.isEmpty())
{
// Get top node of q2 queue
temp = q2.peek();
record.append(temp!.data);
if (temp!.left  != nil)
{
q1.enqueue(temp!.left);
}
if (temp!.right  != nil)
{
q1.enqueue(temp!.right);
}
// Remove top element of q2 queue
q2.dequeue();
}
self.printMiddleNode(record);
record.removeAll();
level += 1;
}
}
}
func main()
{
let tree: BinaryTree = BinaryTree();
/*
Create Binary Tree
-----------------
-6
/   \
4    -7
/ \     \
2   3     12
/ \   /  \
10 -4 5    9
/     \      \
1      7      8
*/
tree.root = TreeNode(-6);
tree.root!.left = TreeNode(4);
tree.root!.left!.right = TreeNode(3);
tree.root!.left!.right!.left = TreeNode(10);
tree.root!.left!.right!.left!.left = TreeNode(1);
tree.root!.left!.right!.right = TreeNode(-4);
tree.root!.left!.right!.right!.right = TreeNode(7);
tree.root!.left!.left = TreeNode(2);
tree.root!.right = TreeNode(-7);
tree.root!.right!.right = TreeNode(12);
tree.root!.right!.right!.left = TreeNode(5);
tree.root!.right!.right!.right = TreeNode(9);
tree.root!.right!.right!.right!.right = TreeNode(8);
tree.middleLevelNode();
}
main();``````

#### input

``````  -6
4  -7
3
-4  5
7``````
``````// Kotlin program for
// Print the middle nodes of each level of a binary tree

// Binary Tree node
class TreeNode
{
var data: Int;
var left: TreeNode ? ;
var right: TreeNode ? ;
constructor(data: Int)
{
// Set node value
this.data = data;
this.left = null;
this.right = null;
}
}
// Queue Node
class QNode
{
var n: TreeNode ? ;
var next: QNode ? ;
constructor(n: TreeNode ? )
{
this.n = n;
this.next = null;
}
}
//Define custom queue class
class MyQueue
{
var front: QNode ? ;
var rear: QNode ? ;
var size: Int;
constructor()
{
this.front = null;
this.rear = null;
this.size = 0;
}
// Add a new node at last of queue
fun enqueue(n: TreeNode ? ): Unit
{
val node: QNode = QNode(n);
if (this.front == null)
{
// When first node of queue
this.front = node;
}
else
{
// Add node at last level
this.rear?.next = node;
}
this.size += 1;
this.rear = node;
}
// Delete front node of queue
fun dequeue(): Unit
{
if (this.front != null)
{
if (this.rear == this.front)
{
this.rear = null;
this.front = null;
}
else
{
this.front = this.front?.next;
}
this.size -= 1;
}
}
fun isSize(): Int
{
return this.size;
}
fun isEmpty(): Boolean
{
if (this.isSize() == 0)
{
return true;
}
return false;
}
fun peek(): TreeNode ?
{
if (this.isSize() == 0)
{
return null;
}
else
{
return this.front?.n;
}
}
}
// Define Binary Tree
class BinaryTree
{
var root: TreeNode ? ;
constructor()
{
this.root = null;
}
// Print the middle element of given level
fun printMiddleNode(level: MutableList<Int> ): Unit
{
if (level.size > 0)
{
val middle: Int = level.size / 2;
if ((level.size % 2) == 0)
{
// When two middle element possible
print("\n " + level[middle - 1]);
print(" " + level[middle]);
}
else
{
print("\n " + level[middle]);
}
}
}
// This is display middle node of each level in binary tree
fun middleLevelNode(): Unit
{
if (this.root == null)
{
// When tree is empty
return;
}
// Auxiliary queue which is capable to contain a tree level nodes
val q1: MyQueue = MyQueue();
val q2: MyQueue = MyQueue();
// Auxiliary temp variable
var temp: TreeNode ? ;
var level: Int = 1;
// It will be use assemble a level node.
var record = mutableListOf<Int>();
// Add first node in q1
q1.enqueue(this.root);
// This loop execute until auxiliary queue q1 and q2 are not empty
while (!q1.isEmpty() || !q2.isEmpty())
{
// Execute loop until q1 queue are not empty
// And store the next level node in q2 queue
while (!q1.isEmpty())
{
// Get top node of q1 queue
temp = q1.peek();
if (temp.left != null)
{
q2.enqueue(temp.left);
}
if (temp.right != null)
{
q2.enqueue(temp.right);
}
// Remove top element of q1 queue
q1.dequeue();
}
this.printMiddleNode(record);
record.clear();
level += 1;
// Execute loop until q2 queue are not empty
// And store the next level node in q1 queue
while (!q2.isEmpty())
{
// Get top node of q2 queue
temp = q2.peek();
if (temp.left != null)
{
q1.enqueue(temp.left);
}
if (temp.right != null)
{
q1.enqueue(temp.right);
}
// Remove top element of q2 queue
q2.dequeue();
}
this.printMiddleNode(record);
record.clear();
level += 1;
}
}
}
fun main(args: Array < String > ): Unit
{
val tree: BinaryTree = BinaryTree();
/*
Create Binary Tree
-----------------
-6
/   \
4    -7
/ \     \
2   3     12
/ \   /  \
10 -4 5    9
/     \      \
1      7      8
*/
tree.root = TreeNode(-6);
tree.root?.left = TreeNode(4);
tree.root?.left?.right = TreeNode(3);
tree.root?.left?.right?.left = TreeNode(10);
tree.root?.left?.right?.left?.left = TreeNode(1);
tree.root?.left?.right?.right = TreeNode(-4);
tree.root?.left?.right?.right?.right = TreeNode(7);
tree.root?.left?.left = TreeNode(2);
tree.root?.right = TreeNode(-7);
tree.root?.right?.right = TreeNode(12);
tree.root?.right?.right?.left = TreeNode(5);
tree.root?.right?.right?.right = TreeNode(9);
tree.root?.right?.right?.right?.right = TreeNode(8);
tree.middleLevelNode();
}``````

#### input

`````` -6
4 -7
3
-4 5
7``````

## Time Complexity

The time complexity of this approach is O(n), where n is the number of nodes in the binary tree. This is because we visit each node exactly once during the level order traversal. The insertion and removal operations in the queues take constant time.

## Comment

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