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# Morris traversal for Preorder

Using Morris Traversal, we can traverse the tree without using stack and recursion. The algorithm for Preorder is almost similar to Morris traversal for Inorder.

1...If left child is null, print the current node data. Move to right child.
….Else, Make the right child of the inorder predecessor point to the current node. Two cases arise:
………a) The right child of the inorder predecessor already points to the current node. Set right child to NULL. Move to right child of current node.
………b) The right child is NULL. Set it to the current node. Print the current node’s data and move to left child of current node.
2...Iterate until the current node is not NULL.

Following is the implementation of the above algorithm.

## C++

 `// C++ program for Morris Preorder traversal ` `#include ` `using` `namespace` `std; `   `class` `node ` `{ ` `    ``public``:` `    ``int` `data; ` `    ``node *left, *right; ` `}; `   `/* Helper function that allocates a new node with the ` `given data and NULL left and right pointers. */` `node* newNode(``int` `data) ` `{ ` `    ``node* temp = ``new` `node();` `    ``temp->data = data; ` `    ``temp->left = temp->right = NULL; ` `    ``return` `temp; ` `} `   `// Preorder traversal without recursion and without stack ` `void` `morrisTraversalPreorder(node* root) ` `{ ` `    ``while` `(root) ` `    ``{ ` `        ``// If left child is null, print the current node data. Move to ` `        ``// right child. ` `        ``if` `(root->left == NULL) ` `        ``{ ` `            ``cout<data<<``" "``; ` `            ``root = root->right; ` `        ``} ` `        ``else` `        ``{ ` `            ``// Find inorder predecessor ` `            ``node* current = root->left; ` `            ``while` `(current->right && current->right != root) ` `                ``current = current->right; `   `            ``// If the right child of inorder predecessor already points to ` `            ``// this node ` `            ``if` `(current->right == root) ` `            ``{ ` `                ``current->right = NULL; ` `                ``root = root->right; ` `            ``} `   `            ``// If right child doesn't point to this node, then print this ` `            ``// node and make right child point to this node ` `            ``else` `            ``{ ` `                ``cout<data<<``" "``; ` `                ``current->right = root; ` `                ``root = root->left; ` `            ``} ` `        ``} ` `    ``} ` `} `   `// Function for Standard preorder traversal ` `void` `preorder(node* root) ` `{ ` `    ``if` `(root) ` `    ``{ ` `        ``cout<data<<``" "``; ` `        ``preorder(root->left); ` `        ``preorder(root->right); ` `    ``} ` `} `   `/* Driver program to test above functions*/` `int` `main() ` `{ ` `    ``node* root = NULL; `   `    ``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->left->left = newNode(8); ` `    ``root->left->left->right = newNode(9); `   `    ``root->left->right->left = newNode(10); ` `    ``root->left->right->right = newNode(11); `   `    ``morrisTraversalPreorder(root); `   `    ``cout<

## C

 `// C program for Morris Preorder traversal` `#include ` `#include `   `struct` `node` `{` `    ``int` `data;` `    ``struct` `node *left, *right;` `};`   `/* Helper function that allocates a new node with the` `   ``given data and NULL left and right pointers. */` `struct` `node* newNode(``int` `data)` `{` `    ``struct` `node* temp = (``struct` `node*) ``malloc``(``sizeof``(``struct` `node));` `    ``temp->data = data;` `    ``temp->left = temp->right = NULL;` `    ``return` `temp;` `}`   `// Preorder traversal without recursion and without stack` `void` `morrisTraversalPreorder(``struct` `node* root)` `{` `    ``while` `(root)` `    ``{` `        ``// If left child is null, print the current node data. Move to` `        ``// right child.` `        ``if` `(root->left == NULL)` `        ``{` `            ``printf``( ``"%d "``, root->data );` `            ``root = root->right;` `        ``}` `        ``else` `        ``{` `            ``// Find inorder predecessor` `            ``struct` `node* current = root->left;` `            ``while` `(current->right && current->right != root)` `                ``current = current->right;`   `            ``// If the right child of inorder predecessor already points to` `            ``// this node` `            ``if` `(current->right == root)` `            ``{` `                ``current->right = NULL;` `                ``root = root->right;` `            ``}`   `            ``// If right child doesn't point to this node, then print this` `            ``// node and make right child point to this node` `            ``else` `            ``{` `                ``printf``(``"%d "``, root->data);` `                ``current->right = root;` `                ``root = root->left;` `            ``}` `        ``}` `    ``}` `}`   `// Function for Standard preorder traversal` `void` `preorder(``struct` `node* root)` `{` `    ``if` `(root)` `    ``{` `        ``printf``( ``"%d "``, root->data);` `        ``preorder(root->left);` `        ``preorder(root->right);` `    ``}` `}`   `/* Driver program to test above functions*/` `int` `main()` `{` `    ``struct` `node* root = NULL;`   `    ``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->left->left = newNode(8);` `    ``root->left->left->right = newNode(9);`   `    ``root->left->right->left = newNode(10);` `    ``root->left->right->right = newNode(11);`   `    ``morrisTraversalPreorder(root);`   `    ``printf``(``"\n"``);` `    ``preorder(root);`   `    ``return` `0;` `}`

## Java

 `// Java program to implement Morris preorder traversal`   `// A binary tree node` `class` `Node {` `    `  `    ``int` `data;` `    ``Node left, right;` `    `  `    ``Node(``int` `item) {` `        ``data = item;` `        ``left = right = ``null``;` `    ``}` `}`   `class` `BinaryTree {` `    `  `    ``Node root;` `    `  `    ``void` `morrisTraversalPreorder()` `    ``{` `        ``morrisTraversalPreorder(root);` `    ``}`   `    ``// Preorder traversal without recursion and without stack` `    ``void` `morrisTraversalPreorder(Node node) {` `        ``while` `(node != ``null``) {`   `            ``// If left child is null, print the current node data. Move to` `            ``// right child.` `            ``if` `(node.left == ``null``) {` `                ``System.out.print(node.data + ``" "``);` `                ``node = node.right;` `            ``} ``else` `{`   `                ``// Find inorder predecessor` `                ``Node current = node.left;` `                ``while` `(current.right != ``null` `&& current.right != node) {` `                    ``current = current.right;` `                ``}`   `                ``// If the right child of inorder predecessor ` `                ``// already points to this node` `                ``if` `(current.right == node) {` `                    ``current.right = ``null``;` `                    ``node = node.right;` `                ``}` ` `  `                ``// If right child doesn't point to this node, then print` `                ``// this node and make right child point to this node` `                ``else` `{` `                    ``System.out.print(node.data + ``" "``);` `                    ``current.right = node;` `                    ``node = node.left;` `                ``}` `            ``}` `        ``}` `    ``}` `    `  `    ``void` `preorder()` `    ``{` `        ``preorder(root);` `    ``}`   `    ``// Function for Standard preorder traversal` `    ``void` `preorder(Node node) {` `        ``if` `(node != ``null``) {` `            ``System.out.print(node.data + ``" "``);` `            ``preorder(node.left);` `            ``preorder(node.right);` `        ``}` `    ``}` `    `  `    ``// Driver programs to test above functions` `    ``public` `static` `void` `main(String args[]) {` `        ``BinaryTree tree = ``new` `BinaryTree();` `        ``tree.root = ``new` `Node(``1``);` `        ``tree.root.left = ``new` `Node(``2``);` `        ``tree.root.right = ``new` `Node(``3``);` `        ``tree.root.left.left = ``new` `Node(``4``);` `        ``tree.root.left.right = ``new` `Node(``5``);` `        ``tree.root.right.left = ``new` `Node(``6``);` `        ``tree.root.right.right = ``new` `Node(``7``);` `        ``tree.root.left.left.left = ``new` `Node(``8``);` `        ``tree.root.left.left.right = ``new` `Node(``9``);` `        ``tree.root.left.right.left = ``new` `Node(``10``);` `        ``tree.root.left.right.right = ``new` `Node(``11``);` `        ``tree.morrisTraversalPreorder();` `        ``System.out.println(``""``);` `        ``tree.preorder();` `        `  `    ``}` `}`   `// this code has been contributed by Mayank Jaiswal`

## Python3

 `# Python program for Morris Preorder traversal`   `# A binary tree Node` `class` `Node:` `    ``def` `__init__(``self``, data):` `        ``self``.data ``=` `data` `        ``self``.left ``=` `None` `        ``self``.right ``=` `None`   `# Preorder traversal without ` `# recursion and without stack` `def` `MorrisTraversal(root):` `    ``curr ``=` `root`   `    ``while` `curr:` `        ``# If left child is null, print the` `        ``# current node data. And, update ` `        ``# the current pointer to right child.` `        ``if` `curr.left ``is` `None``:` `            ``print``(curr.data, end``=` `" "``)` `            ``curr ``=` `curr.right`   `        ``else``:` `            ``# Find the inorder predecessor` `            ``prev ``=` `curr.left`   `            ``while` `prev.right ``is` `not` `None` `and` `prev.right ``is` `not` `curr:` `                ``prev ``=` `prev.right`   `            ``# If the right child of inorder` `            ``# predecessor already points to` `            ``# the current node, update the ` `            ``# current with it's right child` `            ``if` `prev.right ``is` `curr:` `                ``prev.right ``=` `None` `                ``curr ``=` `curr.right` `                `  `            ``# else If right child doesn't point` `            ``# to the current node, then print this` `            ``# node's data and update the right child` `            ``# pointer with the current node and update` `            ``# the current with it's left child` `            ``else``:` `                ``print` `(curr.data, end``=``" "``)` `                ``prev.right ``=` `curr ` `                ``curr ``=` `curr.left`   `# Function for Standard preorder traversal` `def` `preorfer(root):` `    ``if` `root :` `        ``print``(root.data, end ``=` `" "``)` `        ``preorfer(root.left)` `        ``preorfer(root.right)` `        `    `# Driver program to test ` `root ``=` `Node(``1``)` `root.left ``=` `Node(``2``)` `root.right ``=` `Node(``3``)`   `root.left.left ``=` `Node(``4``)` `root.left.right ``=` `Node(``5``)`   `root.right.left``=` `Node(``6``)` `root.right.right ``=` `Node(``7``)`   `root.left.left.left ``=` `Node(``8``)` `root.left.left.right ``=` `Node(``9``)`   `root.left.right.left ``=` `Node(``10``)` `root.left.right.right ``=` `Node(``11``)`     `MorrisTraversal(root)` `print``(``"\n"``)` `preorfer(root)`     `# This code is contributed by 'Aartee'`

## C#

 `// C# program to implement Morris` `// preorder traversal ` `using` `System;`   `// A binary tree node ` `public` `class` `Node` `{` `    ``public` `int` `data;` `    ``public` `Node left, right;`   `    ``public` `Node(``int` `item)` `    ``{` `        ``data = item;` `        ``left = right = ``null``;` `    ``}` `}`   `class` `GFG` `{` `public` `Node root;`   `public` `virtual` `void` `morrisTraversalPreorder()` `{` `    ``morrisTraversalPreorder(root);` `}`   `// Preorder traversal without ` `// recursion and without stack ` `public` `virtual` `void` `morrisTraversalPreorder(Node node)` `{` `    ``while` `(node != ``null``)` `    ``{`   `        ``// If left child is null, print the ` `        ``// current node data. Move to right child. ` `        ``if` `(node.left == ``null``)` `        ``{` `            ``Console.Write(node.data + ``" "``);` `            ``node = node.right;` `        ``}` `        ``else` `        ``{`   `            ``// Find inorder predecessor ` `            ``Node current = node.left;` `            ``while` `(current.right != ``null` `&& ` `                   ``current.right != node)` `            ``{` `                ``current = current.right;` `            ``}`   `            ``// If the right child of inorder predecessor ` `            ``// already points to this node ` `            ``if` `(current.right == node)` `            ``{` `                ``current.right = ``null``;` `                ``node = node.right;` `            ``}`   `            ``// If right child doesn't point to ` `            ``// this node, then print this node ` `            ``// and make right child point to this node ` `            ``else` `            ``{` `                ``Console.Write(node.data + ``" "``);` `                ``current.right = node;` `                ``node = node.left;` `            ``}` `        ``}` `    ``}` `}`   `public` `virtual` `void` `preorder()` `{` `    ``preorder(root);` `}`   `// Function for Standard preorder traversal ` `public` `virtual` `void` `preorder(Node node)` `{` `    ``if` `(node != ``null``)` `    ``{` `        ``Console.Write(node.data + ``" "``);` `        ``preorder(node.left);` `        ``preorder(node.right);` `    ``}` `}`   `// Driver Code` `public` `static` `void` `Main(``string``[] args)` `{` `    ``GFG tree = ``new` `GFG();` `    ``tree.root = ``new` `Node(1);` `    ``tree.root.left = ``new` `Node(2);` `    ``tree.root.right = ``new` `Node(3);` `    ``tree.root.left.left = ``new` `Node(4);` `    ``tree.root.left.right = ``new` `Node(5);` `    ``tree.root.right.left = ``new` `Node(6);` `    ``tree.root.right.right = ``new` `Node(7);` `    ``tree.root.left.left.left = ``new` `Node(8);` `    ``tree.root.left.left.right = ``new` `Node(9);` `    ``tree.root.left.right.left = ``new` `Node(10);` `    ``tree.root.left.right.right = ``new` `Node(11);` `    ``tree.morrisTraversalPreorder();` `    ``Console.WriteLine(``""``);` `    ``tree.preorder();` `}` `}`   `// This code is contributed by Shrikant13`

## Javascript

 ``

Output

```1 2 4 8 9 5 10 11 3 6 7
1 2 4 8 9 5 10 11 3 6 7 ```

Time Complexity: O(n), we visit every node at most once.
Auxiliary Space: O(1), we use a constant amount of space for variables and pointers.

Limitations:
Morris’s traversal modifies the tree during the process. It establishes the right links while moving down the tree and resets the right links while moving up the tree. So the algorithm cannot be applied if write operations are not allowed.