Given a Binary Tree, the task is to perform Specific Level Order Traversal of the tree such that at each level print 1st element then the last element, then 2nd element and 2nd last element, until all elements of that level is printed and so on.

**Examples:**

Input:Below is the given tree:

Output:1 8 3 4 7 5 6

Explanation:

1st level: 1(root)

2nd level: 8(left), 3(right)

3rd level: 4(left), 7(right), 5(left), 6(right)

Input:Below is the given tree:

Output:20 8 22 4 12 10 14

Explanation:

1st level: 20(root)

2nd level: 8(left), 22(right)

3rd level: 4(left), 12(right)

4th level: 10(left), 14(right)

**Approach:** The idea is to the Level Order Traversal of the given Binary Tree and convert this tree into Perfect Binary Tree. While traversing if any node whose **child Node** doesn’t exist then append **NULL** node as the child node in the queue. Below are the steps:

- Perform the level order traversal of the given tree.
- During traveral if any node whose
**child Node**doesn’t exist then append**NULL**node as the child node in the queue - During traversal for each level do the following:
- Maintain two queues to store the nodes for the two half of each level.
- For first half of the level store nodes in left to right manner.
- For second half of the level store nodes in right to left manner.
- Iterate the above two queues formed and print in an alternate manner for specific level order traversal.

Below is the implementation of the above approach:

## Python3

`# Python program for the above approach ` `from` `queue ` `import` `Queue ` ` ` `# A binary tree node ` `class` `Node: ` ` ` ` ` `# A constructor for making ` ` ` `# a new node ` ` ` `def` `__init__(` `self` `, key): ` ` ` `self` `.data ` `=` `key ` ` ` `self` `.left ` `=` `None` ` ` `self` `.right ` `=` `None` ` ` `# Function to find the height of tree ` `def` `Height(root): ` ` ` `if` `root ` `=` `=` `None` `: ` ` ` `return` `0` ` ` `return` `1` `+` `max` `(Height(root.left), Height(root.right)) ` ` ` ` ` `# Given a perfect binary tree ` `# print its node in Specific order ` `def` `printSpecificLevelOrder(A, B, height): ` ` ` ` ` `while` `height !` `=` `0` `: ` ` ` ` ` `# Get each one front ` ` ` `# element of both queue ` ` ` `X ` `=` `A.get() ` ` ` `Y ` `=` `B.get() ` ` ` ` ` `# Check if X exist or not ` ` ` `if` `X ` `=` `=` `None` `: ` ` ` `# Assume is has and put ` ` ` `# their both child as none ` ` ` `A.put(` `None` `) ` ` ` `A.put(` `None` `) ` ` ` `else` `: ` ` ` `# print the data and store ` ` ` `# their child first left ` ` ` `# then right ` ` ` `print` `(X.data, end ` `=` `" "` `) ` ` ` `A.put(X.left) ` ` ` `A.put(X.right) ` ` ` ` ` `# Check Y exist or not ` ` ` `if` `Y ` `=` `=` `None` `: ` ` ` `# Assume is has and put ` ` ` `# their both child as none ` ` ` `B.put(` `None` `) ` ` ` `B.put(` `None` `) ` ` ` `else` `: ` ` ` `# print the data and store their ` ` ` `# child first left then right ` ` ` `print` `(Y.data, end ` `=` `" "` `) ` ` ` `B.put(Y.right) ` ` ` `B.put(Y.left) ` ` ` `# Decrease by 1 unit ` ` ` `height` `-` `=` `1` ` ` ` ` `# Driver Code ` ` ` `# Given Tree ` `root ` `=` `Node(` `1` `) ` ` ` `root.left ` `=` `Node(` `2` `) ` `root.right ` `=` `Node(` `3` `) ` ` ` ` ` `root.left.left ` `=` `Node(` `4` `) ` `root.left.right ` `=` `Node(` `5` `) ` `root.right.right ` `=` `Node(` `7` `) ` ` ` `root.left.left.left ` `=` `Node(` `8` `) ` `root.left.left.right ` `=` `Node(` `9` `) ` `root.left.right.left ` `=` `Node(` `10` `) ` `root.left.right.right ` `=` `Node(` `11` `) ` `root.right.right.left ` `=` `Node(` `14` `) ` `root.right.right.right ` `=` `Node(` `15` `) ` ` ` `root.left.left.left.left ` `=` `Node(` `16` `) ` `root.left.left.left.right ` `=` `Node(` `17` `) ` `root.left.left.right.left ` `=` `Node(` `18` `) ` `root.left.left.right.right ` `=` `Node(` `19` `) ` `root.left.right.left.left ` `=` `Node(` `20` `) ` `root.left.right.left.right ` `=` `Node(` `21` `) ` `root.left.right.right.left ` `=` `Node(` `22` `) ` `root.left.right.right.right ` `=` `Node(` `23` `) ` `root.right.right.left.left ` `=` `Node(` `28` `) ` `root.right.right.left.right ` `=` `Node(` `29` `) ` `root.right.right.right.left ` `=` `Node(` `30` `) ` `root.right.right.right.right ` `=` `Node(` `31` `) ` ` ` `# Initialise Queue ` `A ` `=` `Queue(` `100` `) ` `B ` `=` `Queue(` `100` `) ` ` ` `# Check top root manually ` `if` `root !` `=` `None` `: ` ` ` `print` `(root.data, end ` `=` `" "` `) ` ` ` ` ` `A.put(root.left) ` ` ` `B.put(root.right) ` ` ` ` ` `height ` `=` `Height(root) ` ` ` `height ` `=` `2` `*` `*` `(height` `-` `1` `)` `-` `1` ` ` `# Function Call ` ` ` `printSpecificLevelOrder(A, B, height) ` |

*chevron_right*

*filter_none*

**Output:**

1 2 3 4 7 5 8 15 9 14 10 11 16 31 17 30 18 29 19 28 20 21 22 23

* Time Complexity:* O(N), N is the number of nodes

*O(N), N is the number of nodes*

**Auxiliary Space:**Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the **DSA Self Paced Course** at a student-friendly price and become industry ready.

## Recommended Posts:

- Perfect Binary Tree Specific Level Order Traversal
- Perfect Binary Tree Specific Level Order Traversal | Set 2
- Level order traversal of Binary Tree using Morris Traversal
- Print a Binary Tree in Vertical Order | Set 3 (Using Level Order Traversal)
- Flatten Binary Tree in order of Level Order Traversal
- Given level order traversal of a Binary Tree, check if the Tree is a Min-Heap
- Insertion in n-ary tree in given order and Level order traversal
- Connect Nodes at same Level (Level Order Traversal)
- Check if the given array can represent Level Order Traversal of Binary Search Tree
- Build Binary Tree from BST such that it's level order traversal prints sorted data
- Density of Binary Tree using Level Order Traversal
- Calculate height of Binary Tree using Inorder and Level Order Traversal
- Check if the level order traversal of a Binary Tree results in a palindrome
- Deletion of a given node K in a Binary Tree using Level Order Traversal
- Boundary Level order traversal of a Binary Tree
- Flatten binary tree in order of post-order traversal
- Construct Full Binary Tree using its Preorder traversal and Preorder traversal of its mirror tree
- Level Order Tree Traversal
- General Tree (Each node can have arbitrary number of children) Level Order Traversal
- Zig Zag Level order traversal of a tree using single array

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.