TheAlgorithms-C-Plus-Plus/data_structure/MorrisInorder.cpp

#include <iostream>
#include <queue>

/**************************
	@author shrutisheoran
**************************/

using namespace std;

struct Btree
{
	int data;
	struct Btree *left;  //Pointer to left subtree
	struct Btree *right; //Pointer to right subtree
};

void insert(Btree **root, int d)
{
	Btree *nn = new Btree(); //Creating new node
	nn->data = d;
	nn->left = NULL;
	nn->right = NULL;
	if (*root == NULL)
	{
		*root = nn;
		return;
	}
	else
	{
		queue<Btree *> q;
		// Adding root node to queue
		q.push(*root);
		while (!q.empty())
		{
			Btree *node = q.front();
			// Removing parent node from queue
			q.pop();
			if (node->left)
				// Adding left child of removed node to queue
				q.push(node->left);
			else
			{
				// Adding new node if no left child is present
				node->left = nn;
				return;
			}
			if (node->right)
				// Adding right child of removed node to queue
				q.push(node->right);
			else
			{
				// Adding new node if no right child is present
				node->right = nn;
				return;
			}
		}
	}
}

void morrisInorder(Btree *root)
{
	Btree *curr = root;
	Btree *temp;
	while (curr)
	{
		if (curr->left == NULL)
		{
			cout << curr->data << " ";
			// If left of current node is NULL then curr is shifted to right
			curr = curr->right;
		}
		else
		{
			// Left of current node is stored in temp
			temp = curr->left;
			// Moving to extreme right of temp
			while (temp->right && temp->right != curr)
				temp = temp->right;
			// If extreme right is null it is made to point to currrent node (will be used for backtracking)
			if (temp->right == NULL)
			{
				temp->right = curr;
				// current node is made to point its left subtree
				curr = curr->left;
			}
			// If extreme right already points to currrent node it it set to null
			else if (temp->right == curr)
			{
				cout << curr->data << " ";
				temp->right = NULL;
				// current node is made to point its right subtree
				curr = curr->right;
			}
		}
	}
}

int main()
{
	// Testing morrisInorder funtion
	Btree *root = NULL;
	int i;
	for (i = 1; i <= 7; i++)
		insert(&root, i);
	cout << "Morris Inorder: ";
	morrisInorder(root);
	return 0;
}