Related Articles

# Print odd positioned nodes of even levels in level order of the given binary tree

• Last Updated : 24 Jun, 2021

Given a binary tree, the task is to print the odd positioned nodes of even levels in the level order traversal of the tree. The root is considered at level 0, and the leftmost node of any level is considered as a node at position 0.
Example:

```Input:
1
/    \
2       3
/ \      /  \
4   5    6    7
/  \
8    9
/      \
10       11
Output: 5 7 11

Input:
2
/   \
4     15
/     /
45   17
Output: 17```

Prerequisite – Even positioned elements at even level
Approach: To print nodes level by level, use level order traversal. The idea is based on Print level order traversal line by line. For that, traverse nodes level by level and switch odd level flag after every level. Similarly, mark 2nd node in every level as odd position and switch it after each time the next node is processed.
Below is the implementation of the above approach:

## C++

 `// C++ implementation of the approach``#include ``using` `namespace` `std;` `struct` `Node {``    ``int` `data;``    ``Node *left, *right;``};` `// Iterative method to do level order``// traversal line by line``void` `printEvenLevelOddNodes(Node* root)``{``    ``// Base Case``    ``if` `(root == NULL)``        ``return``;` `    ``// Create an empty queue for level``    ``// order traversal``    ``queue q;` `    ``// Enqueue root and initialize level as even``    ``q.push(root);``    ``bool` `evenLevel = ``true``;` `    ``while` `(1) {` `        ``// nodeCount (queue size) indicates``        ``// number of nodes in the current level``        ``int` `nodeCount = q.size();``        ``if` `(nodeCount == 0)``            ``break``;` `        ``// Mark 1st node as even positioned``        ``bool` `evenNodePosition = ``true``;` `        ``// Dequeue all the nodes of current level``        ``// and Enqueue all the nodes of next level``        ``while` `(nodeCount > 0) {``            ``Node* node = q.front();` `            ``// Print only even positioned``            ``// nodes of even levels``            ``if` `(evenLevel && !evenNodePosition)``                ``cout << node->data << ``" "``;``            ``q.pop();``            ``if` `(node->left != NULL)``                ``q.push(node->left);``            ``if` `(node->right != NULL)``                ``q.push(node->right);``            ``nodeCount--;` `            ``// Switch the even position flag``            ``evenNodePosition = !evenNodePosition;``        ``}` `        ``// Switch the even level flag``        ``evenLevel = !evenLevel;``    ``}``}` `// Utility method to create a node``struct` `Node* newNode(``int` `data)``{``    ``struct` `Node* node = ``new` `Node;``    ``node->data = data;``    ``node->left = node->right = NULL;``    ``return` `(node);``}` `// Driver code``int` `main()``{``    ``struct` `Node* root = newNode(1);``    ``root->left = newNode(2);``    ``root->right = newNode(3);``    ``root->left->left = newNode(4);``    ``root->left->right = newNode(5);``    ``root->right->left = newNode(6);``    ``root->right->right = newNode(7);``    ``root->left->right->left = newNode(8);``    ``root->left->right->right = newNode(9);``    ``root->left->right->left->left = newNode(10);``    ``root->left->right->right->right = newNode(11);` `    ``printEvenLevelOddNodes(root);` `    ``return` `0;``}`

## Java

 `// Java implementation of the above approach``import` `java.util.*;``class` `GFG``{` `static` `class` `Node``{``    ``int` `data;``    ``Node left, right;``};` `// Iterative method to do level order``// traversal line by line``static` `void` `printEvenLevelOddNodes(Node root)``{``    ``// Base Case``    ``if` `(root == ``null``)``        ``return``;` `    ``// Create an empty queue for level``    ``// order traversal``    ``Queue q = ``new` `LinkedList<>();` `    ``// Enqueue root and initialize level as even``    ``q.add(root);``    ``boolean` `evenLevel = ``true``;` `    ``while` `(``true``)``    ``{` `        ``// nodeCount (queue size) indicates``        ``// number of nodes in the current level``        ``int` `nodeCount = q.size();``        ``if` `(nodeCount == ``0``)``            ``break``;` `        ``// Mark 1st node as even positioned``        ``boolean` `evenNodePosition = ``true``;` `        ``// Dequeue all the nodes of current level``        ``// and Enqueue all the nodes of next level``        ``while` `(nodeCount > ``0``)``        ``{``            ``Node node = q.peek();` `            ``// Print only even positioned``            ``// nodes of even levels``            ``if` `(evenLevel && !evenNodePosition)``                ``System.out.print(node.data + ``" "``);` `            ``q.remove();``            ``if` `(node.left != ``null``)``                ``q.add(node.left);``            ``if` `(node.right != ``null``)``                ``q.add(node.right);``            ``nodeCount--;` `            ``// Switch the even position flag``            ``evenNodePosition = !evenNodePosition;``        ``}` `        ``// Switch the even level flag``        ``evenLevel = !evenLevel;``    ``}``}` `// Utility method to create a node``static` `Node newNode(``int` `data)``{``    ``Node node = ``new` `Node();``    ``node.data = data;``    ``node.left = node.right = ``null``;``    ``return` `(node);``}` `// Driver code``public` `static` `void` `main(String[] args)``{``    ``Node root = newNode(``1``);``    ``root.left = newNode(``2``);``    ``root.right = newNode(``3``);``    ``root.left.left = newNode(``4``);``    ``root.left.right = newNode(``5``);``    ``root.right.left = newNode(``6``);``    ``root.right.right = newNode(``7``);``    ``root.left.right.left = newNode(``8``);``    ``root.left.right.right = newNode(``9``);``    ``root.left.right.left.left = newNode(``10``);``    ``root.left.right.right.right = newNode(``11``);` `    ``printEvenLevelOddNodes(root);``}``}` `// This code is contributed by Princi Singh`

## Python3

 `# Python implementation of the approach` `# Utility method to create a node``class` `newNode:` `    ``# Construct to create a new node``    ``def` `__init__(``self``, key):``        ``self``.data ``=` `key``        ``self``.left ``=` `None``        ``self``.right ``=` `None` `# Iterative method to do level order``# traversal line by line``def` `printEvenLevelOddNodes(root):``    ``# Base Case``    ``if` `(root ``=``=` `None``):``        ``return``    ` `    ``# Create an empty queue for level``    ``# order traversal``    ``q ``=``[]``    ` `    ``# Enqueue root and initialize level as even``    ``q.append(root)``    ``evenLevel ``=` `True``    ` `    ``while` `(``1``):``        ` `        ``# nodeCount (queue size) indicates``        ``# number of nodes in the current level``        ``nodeCount ``=` `len``(q)``        ``if` `(nodeCount ``=``=` `0``):``            ``break``        ` `        ``# Mark 1st node as even positioned``        ``evenNodePosition ``=` `True``        ` `        ``# Dequeue all the nodes of current level``        ``# and Enqueue all the nodes of next level``        ``while` `(nodeCount > ``0``):``            ``node ``=` `q[``0``]``            ``# Pronly even positioned``            ``# nodes of even levels``            ``if` `evenLevel ``and` `not` `evenNodePosition:``                ``print``(node.data, end ``=``" "``)``            ``q.pop(``0``)``            ``if` `(node.left !``=` `None``):``                ``q.append(node.left)``            ``if` `(node.right !``=` `None``):``                ``q.append(node.right)``            ``nodeCount``-``=` `1``            ` `            ``# Switch the even position flag``            ``evenNodePosition ``=` `not` `evenNodePosition``        ` `        ``# Switch the even level flag``        ``evenLevel ``=` `not` `evenLevel``    `   `# Driver code``if` `__name__ ``=``=` `'__main__'``:``    ` `    ``root ``=` `newNode(``1``)``    ``root.left ``=` `newNode(``2``)``    ``root.right ``=` `newNode(``3``)``    ``root.left.left ``=` `newNode(``4``)``    ``root.left.right ``=` `newNode(``5``)``    ``root.right.left ``=` `newNode(``6``)``    ``root.right.right ``=` `newNode(``7``)``    ``root.left.right.left ``=` `newNode(``8``)``    ``root.left.right.right ``=` `newNode(``9``)``    ``root.left.right.left.left ``=` `newNode(``10``)``    ``root.left.right.right.right ``=` `newNode(``11``)` `    ``printEvenLevelOddNodes(root)`

## C#

 `// C# implementation of the above approach``using` `System;``using` `System.Collections.Generic;``    ` `class` `GFG``{``public` `class` `Node``{``    ``public` `int` `data;``    ``public` `Node left, right;``};` `// Iterative method to do level order``// traversal line by line``static` `void` `printEvenLevelOddNodes(Node root)``{``    ``// Base Case``    ``if` `(root == ``null``)``        ``return``;` `    ``// Create an empty queue for level``    ``// order traversal``    ``Queue q = ``new` `Queue();` `    ``// Enqueue root and initialize level as even``    ``q.Enqueue(root);``    ``bool` `evenLevel = ``true``;` `    ``while` `(``true``)``    ``{` `        ``// nodeCount (queue size) indicates``        ``// number of nodes in the current level``        ``int` `nodeCount = q.Count;``        ``if` `(nodeCount == 0)``            ``break``;` `        ``// Mark 1st node as even positioned``        ``bool` `evenNodePosition = ``true``;` `        ``// Dequeue all the nodes of current level``        ``// and Enqueue all the nodes of next level``        ``while` `(nodeCount > 0)``        ``{``            ``Node node = q.Peek();` `            ``// Print only even positioned``            ``// nodes of even levels``            ``if` `(evenLevel && !evenNodePosition)``                ``Console.Write(node.data + ``" "``);` `            ``q.Dequeue();``            ``if` `(node.left != ``null``)``                ``q.Enqueue(node.left);``            ``if` `(node.right != ``null``)``                ``q.Enqueue(node.right);``            ``nodeCount--;` `            ``// Switch the even position flag``            ``evenNodePosition = !evenNodePosition;``        ``}` `        ``// Switch the even level flag``        ``evenLevel = !evenLevel;``    ``}``}` `// Utility method to create a node``static` `Node newNode(``int` `data)``{``    ``Node node = ``new` `Node();``    ``node.data = data;``    ``node.left = node.right = ``null``;``    ``return` `(node);``}` `// Driver code``public` `static` `void` `Main(String[] args)``{``    ``Node root = newNode(1);``    ``root.left = newNode(2);``    ``root.right = newNode(3);``    ``root.left.left = newNode(4);``    ``root.left.right = newNode(5);``    ``root.right.left = newNode(6);``    ``root.right.right = newNode(7);``    ``root.left.right.left = newNode(8);``    ``root.left.right.right = newNode(9);``    ``root.left.right.left.left = newNode(10);``    ``root.left.right.right.right = newNode(11);` `    ``printEvenLevelOddNodes(root);``}``}` `// This code is contributed by 29AjayKumar`

## Javascript

 ``
Output:
`5 7 11`

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.  To complete your preparation from learning a language to DS Algo and many more,  please refer Complete Interview Preparation Course.

In case you wish to attend live classes with experts, please refer DSA Live Classes for Working Professionals and Competitive Programming Live for Students.

My Personal Notes arrow_drop_up