# Level order traversal using queue in php

Php program for Level order traversal using queue. Here problem description and other solutions.

```
<?php
/*
Php program for
Level order tree traversal using queue
*/
// Create Q node
class QNode
{
public $data;
public $next;
function __construct($node)
{
$this->data = $node;
$this->next = NULL;
}
}
// 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;
}
}
class MyQueue
{
public $head;
public $tail;
public $count;
public function __construct()
{
$this->head = NULL;
$this->tail = NULL;
$this->count = 0;
}
public function size()
{
return $this->count;
}
public function isEmpty()
{
return $this->count == 0;
}
// Add new node of queue
public function enqueue($value)
{
// Create a new node
$node = new QNode($value);
if ($this->head == NULL)
{
// Add first element into queue
$this->head = $node;
}
else
{
// Add node at the end using tail
$this->tail->next = $node;
}
$this->count++;
$this->tail = $node;
}
// Delete a element into queue
function dequeue()
{
if ($this->head == NULL)
{
// Empty Queue
return;
}
// Visit next node
$this->head = $this->head->next;
$this->count--;
if ($this->head == NULL)
{
// When deleting a last node of linked list
$this->tail = NULL;
}
}
// Get front node
public function peek()
{
if ($this->head == NULL)
{
return NULL;
}
return $this->head->data;
}
}
class BinaryTree
{
public $root;
public function __construct()
{
$this->root = NULL;
}
public function levelOrder()
{
if ($this->root != NULL)
{
$q = new MyQueue();
// Add first node
$q->enqueue($this->root);
$node = $this->root;
while ($q->isEmpty() == false && $node != NULL)
{
if ($node->left != NULL)
{
// Add left child node
$q->enqueue($node->left);
}
if ($node->right != NULL)
{
// Add right child node
$q->enqueue($node->right);
}
// Display level node
echo " ".strval($node->data);
// Remove current node
$q->dequeue();
// Get new head
$node = $q->peek();
}
}
else
{
echo "Empty Tree", "\n";
}
}
public static
function main($args)
{
// Create new tree
$tree = new BinaryTree();
/*
Make A Binary Tree
-----------------------
1
/ \
2 3
/ / \
4 5 6
/ / \
7 8 9
*/
// Adding tree nodes
$tree->root = new TreeNode(1);
$tree->root->left = new TreeNode(2);
$tree->root->right = new TreeNode(3);
$tree->root->right->right = new TreeNode(6);
$tree->root->right->left = new TreeNode(5);
$tree->root->left->left = new TreeNode(4);
$tree->root->left->left->left = new TreeNode(7);
$tree->root->right->left->left = new TreeNode(8);
$tree->root->right->left->right = new TreeNode(9);
// Display level order element
$tree->levelOrder();
}
}
BinaryTree::main(array());
```

**Output**

` 1 2 3 4 5 6 7 8 9`

Please share your knowledge to improve code and content standard. Also submit your doubts, and test case. We improve by your feedback. We will try to resolve your query as soon as possible.

## New Comment