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

Given a binary tree, the task is to print the odd positioned nodes of odd 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: 3 9

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

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

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` `printOddLevelOddNodes(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); ` ` `  `    ``printOddLevelOddNodes(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` `printOddLevelOddNodes(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``); ` ` `  `    ``printOddLevelOddNodes(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` `printOddLevelOddNodes(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` `not` `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``) ` ` `  `    ``printOddLevelOddNodes(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` `printOddLevelOddNodes(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); ` ` `  `    ``printOddLevelOddNodes(root); ` `} ` `} ` ` `  `// This code is contributed by 29AjayKumar `

Output:

```3 9
```

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