#include <stdio.h> 
#include <stdlib.h> 

/* A binary tree tNode has data, pointer to left child 
and a pointer to right child */
struct traversalNode { 
	int data; 
	struct traversalNode* left; 
	struct traversalNode* right; 
}; 

/* Function to traverse binary tree without recursion and 
without stack */
void MorrisTraversal(struct traversalNode* root) 
{ 
	struct traversalNode *current, *pre; 

	if (root == NULL) 
		return; 

	current = root; 
	while (current != NULL) { 

		if (current->left == NULL) { 
			printf("%d ", current->data); 
			current = current->right; 
		} 
		else { 

			/* Find the inorder predecessor of current */
			pre = current->left; 
			while (pre->right != NULL && pre->right != current) 
				pre = pre->right; 

			/* Make current as right child of its inorder 
			predecessor */
			if (pre->right == NULL) { 
				pre->right = current; 
				current = current->left; 
			} 

			/* Revert the changes made in if part to restore 
			the original tree i.e., fix the right child 
			of predecssor */
			else { 
				pre->right = NULL; 
				printf("%d ", current->data); 
				current = current->right; 
			} /* End of if condition pre->right == NULL */
		} /* End of if condition current->left == NULL*/
	} /* End of while */
} 

/* UTILITY FUNCTIONS */
/* Helper function that allocates a new tNode with the 
given data and NULL left and right pointers. */
struct traversalNode* newtraversalNode(int data) 
{ 
	struct traversalNode* node = new traversalNode; 
	node->data = data; 
	node->left = NULL; 
	node->right = NULL; 

	return (node); 
} 

/* Driver program to test above functions*/
int main() 
{ 

	/* Constructed binary tree is 
			12 
		/ \ 
		13	 14 
	/ \ 
	15	 16 
*/
	struct traversalNode* root = newtraversalNode(12); 
	root->left = newtraversalNode(13); 
	root->right = newtraversalNode(14); 
	root->left->left = newtraversalNode(15); 
	root->left->right = newtraversalNode(16); 

	MorrisTraversal(root); 

	return 0; 
}