Inorder Tree Traversal Without Recursion In C++

March 3, 2023

Inorder Tree Traversal Without Recursion

There are three types of traversals in trees: Preorder, Inorder and Postorder. The traversals can be performed using recursion or stack. In this article, inorder traversal is performed using stacks.

More About Inorder Traversal:

Inorder Traversal is a depth first algorithm.
In Inorder Traversal, we first move to the left subtree, then print the node and finally move to the right subtree.
If you want the orginal sequence or how the tree was made, we use the inorder sequence.
Inorder Traversal of a binary search tree gives the sequence in non decreasing order.

Algorithm:

Return if root is empty.
Store temp as root.
Continue the while loop until temp is not null or stack is not empty.
Keep adding the left child of temp until NULL is encountered.
Print the temp node.
Since all the left children are visited, change temp to its right child.

What is Inorder generally used for?

We generally use Inorder traversal technique on Binary Tress , as it fetches the values from the underlying set in order. Using Post-order traversal is also an option, but during post order traversal while delete or freeing nodes it can even delete or free an entire binary tree, which is not a favorable condition.

Inorder Postorder Preorder Traversal Examples

Preorder Tree Traversal in Binary Tree

Postorder Tree Traversal in Binary Tree

Preorder Tree Traversal without Recursion

Postorder Tree Traversal without Recursion

Algorithm To Find Inorder Traversal:

If root is NULL, return NULL.
Visit the left subtree.
Print the node.
Visit the right subtree.

Code Implementation for Inorder Tree traversal

Run

#include<bits/stdc++.h>
using namespace std;

struct Node
{
	int data;
	struct Node* left;
	struct Node* right;
	Node (int data)
	{
		this->data = data;
		left = right = NULL;
	}
};

void inOrder(struct Node *root)
{
	stack s;
	Node *curr = root;

	while (curr != NULL || s.empty() == false)
	{
		while (curr != NULL)
		{
			s.push(curr);
			curr = curr->left;
		}

		curr = s.top();
		s.pop();

		cout << curr->data << " ";
		curr = curr->right;

	} 
}

int main()
{

	struct Node *root = new Node(1);
	root->left	 = new Node(2);
	root->right	 = new Node(3);
	root->left->left = new Node(4);
	root->left->right = new Node(5);

	inOrder(root);
	return 0;
}

Output:
4 2 5 1 3

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