# Level order traversal using queue in python

Python program for Level order traversal using queue. Here problem description and explanation.

```
# Python 3 program for
# Level order tree traversal using queue
# Create Q node
class QNode :
def __init__(self, node) :
self.data = node
self.next = None
# Binary Tree Node
class TreeNode :
def __init__(self, data) :
# Set node value
self.data = data
self.left = None
self.right = None
class MyQueue :
def __init__(self) :
self.head = None
self.tail = None
self.count = 0
def size(self) :
return self.count
def isEmpty(self) :
return self.count == 0
# Add new node of queue
def enqueue(self, value) :
# Create a new node
node = QNode(value)
if (self.head == None) :
# Add first element into queue
self.head = node
else :
# Add node at the end using tail
self.tail.next = node
self.count += 1
self.tail = node
# Delete a element into queue
def dequeue(self) :
if (self.head == None) :
# Empty Queue
return
# Visit next node
self.head = self.head.next
self.count -= 1
if (self.head == None) :
# When deleting a last node of linked list
self.tail = None
# Get front node
def peek(self) :
if (self.head == None) :
return None
return self.head.data
class BinaryTree :
def __init__(self) :
self.root = None
def levelOrder(self) :
if (self.root != None) :
q = MyQueue()
# Add first node
q.enqueue(self.root)
node = self.root
while (q.isEmpty() == False and node != None) :
if (node.left != None) :
# Add left child node
q.enqueue(node.left)
if (node.right != None) :
# Add right child node
q.enqueue(node.right)
# Display level node
print(node.data, end = " ")
# Remove current node
q.dequeue()
# Get new head
node = q.peek()
else :
print("Empty Tree")
def main() :
# Create new tree
tree = BinaryTree()
# Make A Binary Tree
# -----------------------
# 1
# / \
# 2 3
# / / \
# 4 5 6
# / / \
# 7 8 9
# Adding tree nodes
tree.root = TreeNode(1)
tree.root.left = TreeNode(2)
tree.root.right = TreeNode(3)
tree.root.right.right = TreeNode(6)
tree.root.right.left = TreeNode(5)
tree.root.left.left = TreeNode(4)
tree.root.left.left.left = TreeNode(7)
tree.root.right.left.left = TreeNode(8)
tree.root.right.left.right = TreeNode(9)
# Display level order element
tree.levelOrder()
if __name__ == "__main__": main()
```

**Output**

`1 2 3 4 5 6 7 8 9`

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