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Level order traversal in spiral form
• Difficulty Level : Medium
• Last Updated : 14 Dec, 2020

Write a function to print spiral order traversal of a tree. For below tree, function should print 1, 2, 3, 4, 5, 6, 7. Method 1 (Recursive)
This problem can be seen as an extension of the level order traversal post.
To print the nodes in spiral order, nodes at different levels should be printed in alternating order. An additional Boolean variable ltr is used to change printing order of levels. If ltr is 1 then printGivenLevel() prints nodes from left to right else from right to left. Value of ltr is flipped in each iteration to change the order.
Function to print level order traversal of tree

```
printSpiral(tree)
bool ltr = 0;
for d = 1 to height(tree)
printGivenLevel(tree, d, ltr);
ltr ~= ltr /*flip ltr*/```

Function to print all nodes at a given level

```printGivenLevel(tree, level, ltr)
if tree is NULL then return;
if level is 1, then
print(tree->data);
else if level greater than 1, then
if(ltr)
printGivenLevel(tree->left, level-1, ltr);
printGivenLevel(tree->right, level-1, ltr);
else
printGivenLevel(tree->right, level-1, ltr);
printGivenLevel(tree->left, level-1, ltr);```

Following is the implementation of above algorithm.

## C++

 `// C++ program for recursive level ``// order traversal in spiral form``#include``using` `namespace` `std;`` ` `// A binary tree node has data, ``// pointer to left child and a``// pointer to right child ``struct` `node``{``    ``int` `data;``    ``struct` `node* left;``    ``struct` `node* right;``};`` ` `// Function protoypes ``void` `printGivenLevel(``struct` `node* root, ``                     ``int` `level, ``int` `ltr);``int` `height(``struct` `node* node);``struct` `node* newNode(``int` `data);`` ` `// Function to print spiral traversal of a tree``void` `printSpiral(``struct` `node* root)``{``    ``int` `h = height(root);``    ``int` `i;`` ` `    ``// ltr -> Left to Right. If this variable``    ``// is set,then the given level is traversed ``    ``// from left to right. ``    ``bool` `ltr = ``false``;``    ``for``(i = 1; i <= h; i++)``    ``{``        ``printGivenLevel(root, i, ltr);`` ` `        ``// Revert ltr to traverse next ``        ``// level in opposite order``        ``ltr = !ltr;``    ``}``}`` ` `// Print nodes at a given level ``void` `printGivenLevel(``struct` `node* root, ``                     ``int` `level, ``int` `ltr)``{``    ``if` `(root == NULL)``        ``return``;``    ``if` `(level == 1)``        ``cout << root->data << ``" "``;``         ` `    ``else` `if` `(level > 1) ``    ``{``        ``if` `(ltr)``        ``{``            ``printGivenLevel(root->left, ``                            ``level - 1, ltr);``            ``printGivenLevel(root->right,``                            ``level - 1, ltr);``        ``}``        ``else` `        ``{``            ``printGivenLevel(root->right, ``                            ``level - 1, ltr);``            ``printGivenLevel(root->left,``                            ``level - 1, ltr);``        ``}``    ``}``}`` ` `// Compute the "height" of a tree -- the number of``// nodes along the longest path from the root node``// down to the farthest leaf node.``int` `height(``struct` `node* node)``{``    ``if` `(node == NULL)``        ``return` `0;``    ``else` `    ``{``         ` `        ``// Compute the height of each subtree ``        ``int` `lheight = height(node->left);``        ``int` `rheight = height(node->right);`` ` `        ``// Use the larger one ``        ``if` `(lheight > rheight)``            ``return` `(lheight + 1);``        ``else``            ``return` `(rheight + 1);``    ``}``}`` ` `// Helper function that allocates a new ``// node with the given data and NULL left``// and right pointers. ``struct` `node* newNode(``int` `data)``{``    ``node* newnode = ``new` `node();``    ``newnode->data = data;``    ``newnode->left = NULL;``    ``newnode->right = NULL;`` ` `    ``return` `(newnode);``}`` ` `// Driver code``int` `main()``{``    ``struct` `node* root = newNode(1);``    ``root->left = newNode(2);``    ``root->right = newNode(3);``    ``root->left->left = newNode(7);``    ``root->left->right = newNode(6);``    ``root->right->left = newNode(5);``    ``root->right->right = newNode(4);``    ``printf``(``"Spiral Order traversal of "` `           ``"binary tree is \n"``);``            ` `    ``printSpiral(root);`` ` `    ``return` `0;``}`` ` `// This code is contributed by samrat2825`

## C

 `// C program for recursive level order traversal in spiral form``#include ``#include ``#include `` ` `/* A binary tree node has data, pointer to left child``   ``and a pointer to right child */``struct` `node {``    ``int` `data;``    ``struct` `node* left;``    ``struct` `node* right;``};`` ` `/* Function protoypes */``void` `printGivenLevel(``struct` `node* root, ``int` `level, ``int` `ltr);``int` `height(``struct` `node* node);``struct` `node* newNode(``int` `data);`` ` `/* Function to print spiral traversal of a tree*/``void` `printSpiral(``struct` `node* root)``{``    ``int` `h = height(root);``    ``int` `i;`` ` `    ``/*ltr -> Left to Right. If this variable is set,``      ``then the given level is traversed from left to right. */``    ``bool` `ltr = ``false``;``    ``for` `(i = 1; i <= h; i++) {``        ``printGivenLevel(root, i, ltr);`` ` `        ``/*Revert ltr to traverse next level in opposite order*/``        ``ltr = !ltr;``    ``}``}`` ` `/* Print nodes at a given level */``void` `printGivenLevel(``struct` `node* root, ``int` `level, ``int` `ltr)``{``    ``if` `(root == NULL)``        ``return``;``    ``if` `(level == 1)``        ``printf``(``"%d "``, root->data);``    ``else` `if` `(level > 1) {``        ``if` `(ltr) {``            ``printGivenLevel(root->left, level - 1, ltr);``            ``printGivenLevel(root->right, level - 1, ltr);``        ``}``        ``else` `{``            ``printGivenLevel(root->right, level - 1, ltr);``            ``printGivenLevel(root->left, level - 1, ltr);``        ``}``    ``}``}`` ` `/* Compute the "height" of a tree -- the number of``    ``nodes along the longest path from the root node``    ``down to the farthest leaf node.*/``int` `height(``struct` `node* node)``{``    ``if` `(node == NULL)``        ``return` `0;``    ``else` `{``        ``/* compute the height of each subtree */``        ``int` `lheight = height(node->left);``        ``int` `rheight = height(node->right);`` ` `        ``/* use the larger one */``        ``if` `(lheight > rheight)``            ``return` `(lheight + 1);``        ``else``            ``return` `(rheight + 1);``    ``}``}`` ` `/* Helper function that allocates a new node with the``   ``given data and NULL left and right pointers. */``struct` `node* newNode(``int` `data)``{``    ``struct` `node* node = (``struct` `node*)``        ``malloc``(``sizeof``(``struct` `node));``    ``node->data = data;``    ``node->left = NULL;``    ``node->right = NULL;`` ` `    ``return` `(node);``}`` ` `/* Driver program to test above functions*/``int` `main()``{``    ``struct` `node* root = newNode(1);``    ``root->left = newNode(2);``    ``root->right = newNode(3);``    ``root->left->left = newNode(7);``    ``root->left->right = newNode(6);``    ``root->right->left = newNode(5);``    ``root->right->right = newNode(4);``    ``printf``(``"Spiral Order traversal of binary tree is \n"``);``    ``printSpiral(root);`` ` `    ``return` `0;``}`

## Java

 `// Java program for recursive level order traversal in spiral form`` ` `/* A binary tree node has data, pointer to left child ``   ``and a pointer to right child */``class` `Node {``    ``int` `data;``    ``Node left, right;`` ` `    ``public` `Node(``int` `d)``    ``{``        ``data = d;``        ``left = right = ``null``;``    ``}``}`` ` `class` `BinaryTree {``    ``Node root;`` ` `    ``// Function to print the spiral traversal of tree``    ``void` `printSpiral(Node node)``    ``{``        ``int` `h = height(node);``        ``int` `i;`` ` `        ``/* ltr -> left to right. If this variable is set then the``           ``given label is traversed from left to right */``        ``boolean` `ltr = ``false``;``        ``for` `(i = ``1``; i <= h; i++) {``            ``printGivenLevel(node, i, ltr);`` ` `            ``/*Revert ltr to traverse next level in opposite order*/``            ``ltr = !ltr;``        ``}``    ``}`` ` `    ``/* Compute the "height" of a tree -- the number of``    ``nodes along the longest path from the root node``    ``down to the farthest leaf node.*/``    ``int` `height(Node node)``    ``{``        ``if` `(node == ``null``)``            ``return` `0``;``        ``else` `{`` ` `            ``/* compute the height of each subtree */``            ``int` `lheight = height(node.left);``            ``int` `rheight = height(node.right);`` ` `            ``/* use the larger one */``            ``if` `(lheight > rheight)``                ``return` `(lheight + ``1``);``            ``else``                ``return` `(rheight + ``1``);``        ``}``    ``}`` ` `    ``/* Print nodes at a given level */``    ``void` `printGivenLevel(Node node, ``int` `level, ``boolean` `ltr)``    ``{``        ``if` `(node == ``null``)``            ``return``;``        ``if` `(level == ``1``)``            ``System.out.print(node.data + ``" "``);``        ``else` `if` `(level > ``1``) {``            ``if` `(ltr != ``false``) {``                ``printGivenLevel(node.left, level - ``1``, ltr);``                ``printGivenLevel(node.right, level - ``1``, ltr);``            ``}``            ``else` `{``                ``printGivenLevel(node.right, level - ``1``, ltr);``                ``printGivenLevel(node.left, level - ``1``, ltr);``            ``}``        ``}``    ``}``    ``/* Driver program to test the 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(``7``);``        ``tree.root.left.right = ``new` `Node(``6``);``        ``tree.root.right.left = ``new` `Node(``5``);``        ``tree.root.right.right = ``new` `Node(``4``);``        ``System.out.println(``"Spiral order traversal of Binary Tree is "``);``        ``tree.printSpiral(tree.root);``    ``}``}`` ` `// This code has been contributed by Mayank Jaiswal(mayank_24)`

## Python3

 `# Python3 program for recursive level order``# traversal in spiral form `` ` `class` `newNode: `` ` `    ``# Construct to create a newNode ``    ``def` `__init__(``self``, key): ``        ``self``.data ``=` `key ``        ``self``.left ``=` `None``        ``self``.right ``=` `None`` ` `""" Function to print spiral traversal of a tree"""``def` `printSpiral(root):`` ` `    ``h ``=` `height(root) ``     ` `    ``"""ltr Left to Right. If this variable ``    ``is set, then the given level is traversed``    ``from left to right. """``    ``ltr ``=` `False``    ``for` `i ``in` `range``(``1``, h ``+` `1``):``     ` `        ``printGivenLevel(root, i, ltr) `` ` `        ``"""Revert ltr to traverse next level``           ``in opposite order"""``        ``ltr ``=` `not` `ltr ``     ` `""" Print nodes at a given level """``def` `printGivenLevel(root, level, ltr):`` ` `    ``if``(root ``=``=` `None``):``        ``return``    ``if``(level ``=``=` `1``):``        ``print``(root.data, end ``=` `" "``) ``    ``elif` `(level > ``1``):``     ` `        ``if``(ltr):``            ``printGivenLevel(root.left, level ``-` `1``, ltr) ``            ``printGivenLevel(root.right, level ``-` `1``, ltr) ``         ` `        ``else``:``            ``printGivenLevel(root.right, level ``-` `1``, ltr) ``            ``printGivenLevel(root.left, level ``-` `1``, ltr) ``         ` `""" Compute the "height" of a tree -- the number of ``    ``nodes along the longest path from the root node ``    ``down to the farthest leaf node."""``def` `height(node):`` ` `    ``if` `(node ``=``=` `None``):``        ``return` `0``    ``else``:``     ` `        ``""" compute the height of each subtree """``        ``lheight ``=` `height(node.left) ``        ``rheight ``=` `height(node.right) `` ` `        ``""" use the larger one """``        ``if` `(lheight > rheight):``            ``return``(lheight ``+` `1``) ``        ``else``:``            ``return``(rheight ``+` `1``) ``     ` `# Driver Code``if` `__name__ ``=``=` `'__main__'``:``    ``root ``=` `newNode(``1``) ``    ``root.left ``=` `newNode(``2``) ``    ``root.right ``=` `newNode(``3``) ``    ``root.left.left ``=` `newNode(``7``) ``    ``root.left.right ``=` `newNode(``6``) ``    ``root.right.left ``=` `newNode(``5``) ``    ``root.right.right ``=` `newNode(``4``) ``    ``print``(``"Spiral Order traversal of binary tree is"``) ``    ``printSpiral(root) ``     ` `# This code is contributed``# by SHUBHAMSINGH10`

## C#

 `// C# program for recursive level``// order traversal in spiral form``using` `System;`` ` `/* A binary tree node has data, ``pointer to left child and a ``pointer to right child */``public` `class` `Node {``    ``public` `int` `data;``    ``public` `Node left, right;`` ` `    ``public` `Node(``int` `d)``    ``{``        ``data = d;``        ``left = right = ``null``;``    ``}``}`` ` `class` `GFG {``    ``public` `Node root;`` ` `    ``// Function to print the spiral``    ``// traversal of tree``    ``public` `virtual` `void` `printSpiral(Node node)``    ``{``        ``int` `h = height(node);``        ``int` `i;`` ` `        ``/* ltr -> left to right. If this ``        ``variable is set then the given``        ``label is traversed from left to right */``        ``bool` `ltr = ``false``;``        ``for` `(i = 1; i <= h; i++) {``            ``printGivenLevel(node, i, ltr);`` ` `            ``/*Revert ltr to traverse next ``              ``level in opposite order*/``            ``ltr = !ltr;``        ``}``    ``}`` ` `    ``/* Compute the "height" of a tree -- the``    ``number of nodes along the longest path ``    ``from the root node down to the farthest ``    ``leaf node.*/``    ``public` `virtual` `int` `height(Node node)``    ``{``        ``if` `(node == ``null``) {``            ``return` `0;``        ``}``        ``else` `{`` ` `            ``/* compute the height of each subtree */``            ``int` `lheight = height(node.left);``            ``int` `rheight = height(node.right);`` ` `            ``/* use the larger one */``            ``if` `(lheight > rheight) {``                ``return` `(lheight + 1);``            ``}``            ``else` `{``                ``return` `(rheight + 1);``            ``}``        ``}``    ``}`` ` `    ``/* Print nodes at a given level */``    ``public` `virtual` `void` `printGivenLevel(Node node,``                                        ``int` `level,``                                        ``bool` `ltr)``    ``{``        ``if` `(node == ``null``) {``            ``return``;``        ``}``        ``if` `(level == 1) {``            ``Console.Write(node.data + ``" "``);``        ``}``        ``else` `if` `(level > 1) {``            ``if` `(ltr != ``false``) {``                ``printGivenLevel(node.left, level - 1, ltr);``                ``printGivenLevel(node.right, level - 1, ltr);``            ``}``            ``else` `{``                ``printGivenLevel(node.right, level - 1, ltr);``                ``printGivenLevel(node.left, level - 1, ltr);``            ``}``        ``}``    ``}`` ` `    ``// 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(7);``        ``tree.root.left.right = ``new` `Node(6);``        ``tree.root.right.left = ``new` `Node(5);``        ``tree.root.right.right = ``new` `Node(4);``        ``Console.WriteLine(``"Spiral order traversal "``                          ``+ ``"of Binary Tree is "``);``        ``tree.printSpiral(tree.root);``    ``}``}`` ` `// This code is contributed by Shrikant13`

Output:

```Spiral Order traversal of binary tree is
1 2 3 4 5 6 7```

Time Complexity: Worst case time complexity of the above method is O(n^2). Worst case occurs in case of skewed trees.

Method 2 (Iterative)
We can print spiral order traversal in O(n) time and O(n) extra space. The idea is to use two stacks. We can use one stack for printing from left to right and other stack for printing from right to left. In every iteration, we have nodes of one level in one of the stacks. We print the nodes, and push nodes of next level in other stack.

## C++

 `// C++ implementation of a O(n) time method for spiral order traversal``#include ``#include ``using` `namespace` `std;`` ` `// Binary Tree node``struct` `node {``    ``int` `data;``    ``struct` `node *left, *right;``};`` ` `void` `printSpiral(``struct` `node* root)``{``    ``if` `(root == NULL)``        ``return``; ``// NULL check`` ` `    ``// Create two stacks to store alternate levels``    ``stack<``struct` `node*> s1; ``// For levels to be printed from right to left``    ``stack<``struct` `node*> s2; ``// For levels to be printed from left to right`` ` `    ``// Push first level to first stack 's1'``    ``s1.push(root);`` ` `    ``// Keep printing while any of the stacks has some nodes``    ``while` `(!s1.empty() || !s2.empty()) {``        ``// Print nodes of current level from s1 and push nodes of``        ``// next level to s2``        ``while` `(!s1.empty()) {``            ``struct` `node* temp = s1.top();``            ``s1.pop();``            ``cout << temp->data << ``" "``;`` ` `            ``// Note that is right is pushed before left``            ``if` `(temp->right)``                ``s2.push(temp->right);``            ``if` `(temp->left)``                ``s2.push(temp->left);``        ``}`` ` `        ``// Print nodes of current level from s2 and push nodes of``        ``// next level to s1``        ``while` `(!s2.empty()) {``            ``struct` `node* temp = s2.top();``            ``s2.pop();``            ``cout << temp->data << ``" "``;`` ` `            ``// Note that is left is pushed before right``            ``if` `(temp->left)``                ``s1.push(temp->left);``            ``if` `(temp->right)``                ``s1.push(temp->right);``        ``}``    ``}``}`` ` `// A utility function to create a new node``struct` `node* newNode(``int` `data)``{``    ``struct` `node* node = ``new` `struct` `node;``    ``node->data = data;``    ``node->left = NULL;``    ``node->right = NULL;`` ` `    ``return` `(node);``}`` ` `int` `main()``{``    ``struct` `node* root = newNode(1);``    ``root->left = newNode(2);``    ``root->right = newNode(3);``    ``root->left->left = newNode(7);``    ``root->left->right = newNode(6);``    ``root->right->left = newNode(5);``    ``root->right->right = newNode(4);``    ``cout << ``"Spiral Order traversal of binary tree is \n"``;``    ``printSpiral(root);`` ` `    ``return` `0;``}`

## Java

 `// Java implementation of an O(n) approach of level order``// traversal in spiral form`` ` `import` `java.util.*;`` ` `// A Binary Tree node``class` `Node {``    ``int` `data;``    ``Node left, right;`` ` `    ``public` `Node(``int` `item)``    ``{``        ``data = item;``        ``left = right = ``null``;``    ``}``}`` ` `class` `BinaryTree {`` ` `    ``static` `Node root;`` ` `    ``void` `printSpiral(Node node)``    ``{``        ``if` `(node == ``null``)``            ``return``; ``// NULL check`` ` `        ``// Create two stacks to store alternate levels``        ``// For levels to be printed from right to left``        ``Stack s1 = ``new` `Stack(); ``        ``// For levels to be printed from left to right``        ``Stack s2 = ``new` `Stack(); `` ` `        ``// Push first level to first stack 's1'``        ``s1.push(node);`` ` `        ``// Keep printing while any of the stacks has some nodes``        ``while` `(!s1.empty() || !s2.empty()) {``            ``// Print nodes of current level from s1 and push nodes of``            ``// next level to s2``            ``while` `(!s1.empty()) {``                ``Node temp = s1.peek();``                ``s1.pop();``                ``System.out.print(temp.data + ``" "``);`` ` `                ``// Note that is right is pushed before left``                ``if` `(temp.right != ``null``)``                    ``s2.push(temp.right);`` ` `                ``if` `(temp.left != ``null``)``                    ``s2.push(temp.left);``            ``}`` ` `            ``// Print nodes of current level from s2 and push nodes of``            ``// next level to s1``            ``while` `(!s2.empty()) {``                ``Node temp = s2.peek();``                ``s2.pop();``                ``System.out.print(temp.data + ``" "``);`` ` `                ``// Note that is left is pushed before right``                ``if` `(temp.left != ``null``)``                    ``s1.push(temp.left);``                ``if` `(temp.right != ``null``)``                    ``s1.push(temp.right);``            ``}``        ``}``    ``}`` ` `    ``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(``7``);``        ``tree.root.left.right = ``new` `Node(``6``);``        ``tree.root.right.left = ``new` `Node(``5``);``        ``tree.root.right.right = ``new` `Node(``4``);``        ``System.out.println(``"Spiral Order traversal of Binary Tree is "``);``        ``tree.printSpiral(root);``    ``}``}`` ` `// This code has been contributed by Mayank Jaiswal(mayank_24)`

## Python3

 `# Python3 implementation of a O(n) time ``# method for spiral order traversal `` ` `# A class to create a new node ``class` `newNode:``    ``def` `__init__(``self``, data):``        ``self``.data ``=` `data ``        ``self``.left ``=` `None``        ``self``.right ``=` `None`` ` `def` `printSpiral(root):``    ``if` `(root ``=``=` `None``):``        ``return` `# None check `` ` `    ``# Create two stacks to store ``    ``# alternate levels ``    ``s1 ``=` `[] ``# For levels to be printed ``            ``# from right to left ``    ``s2 ``=` `[] ``# For levels to be printed ``            ``# from left to right `` ` `    ``# append first level to first stack 's1' ``    ``s1.append(root) `` ` `    ``# Keep printing while any of the ``    ``# stacks has some nodes ``    ``while` `not` `len``(s1) ``=``=` `0` `or` `not` `len``(s2) ``=``=` `0``:``         ` `        ``# Print nodes of current level from s1 ``        ``# and append nodes of next level to s2 ``        ``while` `not` `len``(s1) ``=``=` `0``:``            ``temp ``=` `s1[``-``1``] ``            ``s1.pop() ``            ``print``(temp.data, end ``=` `" "``) `` ` `            ``# Note that is right is appended``            ``# before left ``            ``if` `(temp.right): ``                ``s2.append(temp.right) ``            ``if` `(temp.left):``                ``s2.append(temp.left)`` ` `        ``# Print nodes of current level from s2 ``        ``# and append nodes of next level to s1 ``        ``while` `(``not` `len``(s2) ``=``=` `0``):``            ``temp ``=` `s2[``-``1``] ``            ``s2.pop() ``            ``print``(temp.data, end ``=` `" "``) `` ` `            ``# Note that is left is appended``            ``# before right ``            ``if` `(temp.left):``                ``s1.append(temp.left) ``            ``if` `(temp.right): ``                ``s1.append(temp.right)`` ` `# Driver Code``if` `__name__ ``=``=` `'__main__'``:``    ``root ``=` `newNode(``1``) ``    ``root.left ``=` `newNode(``2``) ``    ``root.right ``=` `newNode(``3``) ``    ``root.left.left ``=` `newNode(``7``) ``    ``root.left.right ``=` `newNode(``6``) ``    ``root.right.left ``=` `newNode(``5``) ``    ``root.right.right ``=` `newNode(``4``) ``    ``print``(``"Spiral Order traversal of"``,``                    ``"binary tree is "``) ``    ``printSpiral(root)`` ` `# This code is contributed by PranchalK `

## C#

 `// C# implementation of an O(n) approach of``// level order traversal in spiral form``using` `System;``using` `System.Collections.Generic;`` ` `// A Binary Tree node``public` `class` `Node {``    ``public` `int` `data;``    ``public` `Node left, right;`` ` `    ``public` `Node(``int` `item)``    ``{``        ``data = item;``        ``left = right = ``null``;``    ``}``}`` ` `public` `class` `BinaryTree {``    ``public` `static` `Node root;`` ` `    ``public` `virtual` `void` `printSpiral(Node node)``    ``{``        ``if` `(node == ``null``) {``            ``return``; ``// NULL check``        ``}`` ` `        ``// Create two stacks to store alternate levels``        ``Stack s1 = ``new` `Stack(); ``// For levels to be printed``        ``// from right to left``        ``Stack s2 = ``new` `Stack(); ``// For levels to be printed``        ``// from left to right`` ` `        ``// Push first level to first stack 's1'``        ``s1.Push(node);`` ` `        ``// Keep printing while any of the``        ``// stacks has some nodes``        ``while` `(s1.Count > 0 || s2.Count > 0) {``            ``// Print nodes of current level from``            ``// s1 and push nodes of next level to s2``            ``while` `(s1.Count > 0) {``                ``Node temp = s1.Peek();``                ``s1.Pop();``                ``Console.Write(temp.data + ``" "``);`` ` `                ``// Note that is right is pushed before left``                ``if` `(temp.right != ``null``) {``                    ``s2.Push(temp.right);``                ``}`` ` `                ``if` `(temp.left != ``null``) {``                    ``s2.Push(temp.left);``                ``}``            ``}`` ` `            ``// Print nodes of current level from s2``            ``// and push nodes of next level to s1``            ``while` `(s2.Count > 0) {``                ``Node temp = s2.Peek();``                ``s2.Pop();``                ``Console.Write(temp.data + ``" "``);`` ` `                ``// Note that is left is pushed before right``                ``if` `(temp.left != ``null``) {``                    ``s1.Push(temp.left);``                ``}``                ``if` `(temp.right != ``null``) {``                    ``s1.Push(temp.right);``                ``}``            ``}``        ``}``    ``}`` ` `    ``// Driver Code``    ``public` `static` `void` `Main(``string``[] args)``    ``{``        ``BinaryTree tree = ``new` `BinaryTree();``        ``BinaryTree.root = ``new` `Node(1);``        ``BinaryTree.root.left = ``new` `Node(2);``        ``BinaryTree.root.right = ``new` `Node(3);``        ``BinaryTree.root.left.left = ``new` `Node(7);``        ``BinaryTree.root.left.right = ``new` `Node(6);``        ``BinaryTree.root.right.left = ``new` `Node(5);``        ``BinaryTree.root.right.right = ``new` `Node(4);``        ``Console.WriteLine(``"Spiral Order traversal of Binary Tree is "``);``        ``tree.printSpiral(root);``    ``}``}`` ` `// This code is contributed by Shrikant13`

Output:

```Spiral Order traversal of binary tree is
1 2 3 4 5 6 7```

Please write comments if you find any bug in the above program/algorithm; or if you want to share more information about spiral traversal.

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