# Find n-th node in Preorder traversal of a Binary Tree

Given a Binary tree and a number N, write a program to find the N-th node in the Preorder traversal of the given Binary tree.

Prerequisite: Tree Traversal

Examples:

```Input:      N = 4
11
/   \
21    31
/   \
41     51
Output: 51
Explanation: Preorder Traversal of given Binary Tree is 11 21 41 51 31,
so 4th node will be 51.

Input:      N = 5
25
/    \
20    30
/    \ /   \
18    22 24   32
Output: 30
```

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

The idea to solve this problem is to do preorder traversal of the given binary tree and keep track of the count of nodes visited while traversing the tree and print the current node when the count becomes equal to N.

## C++

 `// C++ program to find n-th node of  ` `// Preorder Traversal of Binary Tree ` `#include ` `using` `namespace` `std; ` ` `  `// Tree node ` `struct` `Node { ` `    ``int` `data; ` `    ``Node *left, *right; ` `}; ` ` `  `// function to create new node ` `struct` `Node* createNode(``int` `item) ` `{ ` `    ``Node* temp = ``new` `Node; ` `    ``temp->data = item; ` `    ``temp->left = NULL; ` `    ``temp->right = NULL; ` ` `  `    ``return` `temp; ` `} ` ` `  `// function to find the N-th node in the preorder ` `// traversal of a given binary tree ` `void` `NthPreordernode(``struct` `Node* root, ``int` `N) ` `{ ` `    ``static` `int` `flag = 0; ` ` `  `    ``if` `(root == NULL) ` `        ``return``; ` ` `  `    ``if` `(flag <= N) { ` `        ``flag++; ` ` `  `        ``// prints the n-th node of preorder traversal ` `        ``if` `(flag == N) ` `            ``cout << root->data; ` ` `  `        ``// left recursion ` `        ``NthPreordernode(root->left, N); ` ` `  `        ``// right recursion ` `        ``NthPreordernode(root->right, N); ` `    ``} ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``// construction of binary tree ` `    ``struct` `Node* root = createNode(25); ` `    ``root->left = createNode(20); ` `    ``root->right = createNode(30); ` `    ``root->left->left = createNode(18); ` `    ``root->left->right = createNode(22); ` `    ``root->right->left = createNode(24); ` `    ``root->right->right = createNode(32); ` ` `  `    ``// nth node ` `    ``int` `N = 6; ` ` `  `    ``// prints n-th found found ` `    ``NthPreordernode(root, N); ` ` `  `    ``return` `0; ` `} `

## Python3

 `# Python program to find n-th node of  ` `# Preorder Traversal of Binary Tree ` ` `  `class` `createNode():  ` ` `  `    ``def` `__init__(``self``, data):  ` `        ``self``.data ``=` `data ` `        ``self``.left ``=` `None` `        ``self``.right ``=` `None` `         `  `         `  `# function to find the N-th node in the preorder  ` `# traversal of a given binary tree ` `flag ``=` `[``0``] ` `def` `NthPreordernode(root, N):  ` `    ``if` `(root ``=``=` `None``): ` `        ``return` ` `  `    ``if` `(flag[``0``] <``=` `N):  ` `        ``flag[``0``] ``+``=` `1` ` `  `        ``# prints the n-th node of preorder traversal  ` `        ``if` `(flag[``0``] ``=``=` `N): ` `            ``print``(root.data) ` ` `  `        ``# left recursion  ` `        ``NthPreordernode(root.left, N)  ` ` `  `        ``# right recursion  ` `        ``NthPreordernode(root.right, N) ` `         `  `# Driver code  ` `if` `__name__ ``=``=` `'__main__'``: ` `     `  `    ``# construction of binary tree  ` `    ``root ``=` `createNode(``25``)  ` `    ``root.left ``=` `createNode(``20``)  ` `    ``root.right ``=` `createNode(``30``)  ` `    ``root.left.left ``=` `createNode(``18``)  ` `    ``root.left.right ``=` `createNode(``22``)  ` `    ``root.right.left ``=` `createNode(``24``)  ` `    ``root.right.right ``=` `createNode(``32``)  ` ` `  `    ``# nth node  ` `    ``N ``=` `6` ` `  `    ``# prints n-th found found  ` `    ``NthPreordernode(root, N) ` ` `  `# This code is contributed by SHUBHAMSINGH10 `

Output:

```24
```

Time Complexity: O(n), where n is the number of nodes in the given binary tree.
Auxiliary Space: O(1)

My Personal Notes arrow_drop_up Check out this Author's contributed articles.

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.

Improved By : SHUBHAMSINGH10

Article Tags :
Practice Tags :

Be the First to upvote.

Please write to us at contribute@geeksforgeeks.org to report any issue with the above content.