# Reverse Clockwise spiral traversal of a binary tree

Given a Binary Tree. The task is to print the circular reverse clockwise spiral order traversal of the given binary tree.

Reverse Clockwise Traversal means to traverse the tree in clockwise direction spirally starting from the bottom instead of top root node.

Examples:

```Input :
1
/  \
2    3
/ \    \
4   5    6
/    / \
7    8   9
Output : 9 8 7 1 6 5 4 2 3

Input :
20
/   \
8     22
/   \  /   \
5     3 4    25
/ \
10  14
Output : 14 10 20 25 4 3 5 8 22
```

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach: The idea is to use two variables i initialized to 1 and j initialized to the height of tree and run a while loop which wont break until i becomes greater than j.

• Use another variable flag and initialize it to 0. Now in the while loop, check a condition that if flag is equal to 0 then traverse the tree from right to left and mark flag as 1 so that next time we traverse the tree from left to right, this is done to maintain the spiral clockwise order of traversal.
• <liThen decrement the value of j so that next time the level just above the current level is visited.

• Also when we will traverse the level from top we will mark flag as 0 so that next time we traverse the tree from right to left and then increment the value of i so that next time we visit the level just below the current level.
• Repeat the whole process until the binary tree is completely traversed.

Below is the implementation of the above approach:

## C++

 `// C++ implementation of the approach ` `#include ` `using` `namespace` `std; ` ` `  `// Binary tree node ` `struct` `Node { ` `    ``struct` `Node* left; ` `    ``struct` `Node* right; ` `    ``int` `data; ` ` `  `    ``Node(``int` `data) ` `    ``{ ` `        ``this``->data = data; ` `        ``this``->left = NULL; ` `        ``this``->right = NULL; ` `    ``} ` `}; ` ` `  `// Recursive Function to find height ` `// of binary tree ` `int` `height(``struct` `Node* root) ` `{ ` `    ``// Base condition ` `    ``if` `(root == NULL) ` `        ``return` `0; ` ` `  `    ``// Compute the height of each subtree ` `    ``int` `lheight = height(root->left); ` `    ``int` `rheight = height(root->right); ` ` `  `    ``// Return the maximum of two ` `    ``return` `max(1 + lheight, 1 + rheight); ` `} ` ` `  `// Function to Print Nodes from left to right ` `void` `leftToRight(``struct` `Node* root, ``int` `level) ` `{ ` `    ``if` `(root == NULL) ` `        ``return``; ` ` `  `    ``if` `(level == 1) ` `        ``cout << root->data << ``" "``; ` ` `  `    ``else` `if` `(level > 1) { ` `        ``leftToRight(root->left, level - 1); ` `        ``leftToRight(root->right, level - 1); ` `    ``} ` `} ` ` `  `// Function to Print Nodes from right to left ` `void` `rightToLeft(``struct` `Node* root, ``int` `level) ` `{ ` `    ``if` `(root == NULL) ` `        ``return``; ` ` `  `    ``if` `(level == 1) ` `        ``cout << root->data << ``" "``; ` ` `  `    ``else` `if` `(level > 1) { ` `        ``rightToLeft(root->right, level - 1); ` `        ``rightToLeft(root->left, level - 1); ` `    ``} ` `} ` ` `  `// Function to print reverse clockwise spiral ` `// traversal of a binary tree ` `void` `ReverseClockWiseSpiral(``struct` `Node* root) ` `{ ` `    ``int` `i = 1; ` `    ``int` `j = height(root); ` ` `  `    ``// Flag to mark a change in the direction ` `    ``// of printing nodes ` `    ``int` `flag = 0; ` `    ``while` `(i <= j) { ` ` `  `        ``// If flag is zero print nodes ` `        ``// from right to left ` `        ``if` `(flag == 0) { ` `            ``rightToLeft(root, j); ` ` `  `            ``// Set the value of flag as zero ` `            ``// so that nodes are next time ` `            ``// printed from left to right ` `            ``flag = 1; ` ` `  `            ``// Decrement j ` `            ``j--; ` `        ``} ` ` `  `        ``// If flag is one print nodes ` `        ``// from left to right ` `        ``else` `{ ` `            ``leftToRight(root, i); ` ` `  `            ``// Set the value of flag as zero ` `            ``// so that nodes are next time ` `            ``// printed from right to left ` `            ``flag = 0; ` ` `  `            ``// Increment i ` `            ``i++; ` `        ``} ` `    ``} ` `} ` ` `  `// Driver code ` `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->right->left = ``new` `Node(6); ` `    ``root->right->right = ``new` `Node(7); ` `    ``root->left->right = ``new` `Node(5); ` ` `  `    ``ReverseClockWiseSpiral(root); ` ` `  `    ``return` `0; ` `} `

## Java

 `// Java implementation of the approach  ` `import` `java.util.*; ` ` `  `class` `GFG ` `{ ` `     `  `// Binary tree node  ` `static` `class` `Node  ` `{  ` `    ``Node left;  ` `    ``Node right;  ` `    ``int` `data;  ` ` `  `    ``Node(``int` `data)  ` `    ``{  ` `        ``this``.data = data;  ` `        ``this``.left = ``null``;  ` `        ``this``.right = ``null``;  ` `    ``}  ` `};  ` ` `  `// Recursive Function to find height  ` `// of binary tree  ` `static` `int` `height( Node root)  ` `{  ` `    ``// Base condition  ` `    ``if` `(root == ``null``)  ` `        ``return` `0``;  ` ` `  `    ``// Compute the height of each subtree  ` `    ``int` `lheight = height(root.left);  ` `    ``int` `rheight = height(root.right);  ` ` `  `    ``// Return the maximum of two  ` `    ``return` `Math.max(``1` `+ lheight, ``1` `+ rheight);  ` `}  ` ` `  `// Function to Print Nodes from left to right  ` `static` `void` `leftToRight( Node root, ``int` `level)  ` `{  ` `    ``if` `(root == ``null``)  ` `        ``return``;  ` ` `  `    ``if` `(level == ``1``)  ` `        ``System.out.print( root.data + ``" "``);  ` ` `  `    ``else` `if` `(level > ``1``) ` `    ``{  ` `        ``leftToRight(root.left, level - ``1``);  ` `        ``leftToRight(root.right, level - ``1``);  ` `    ``}  ` `}  ` ` `  `// Function to Print Nodes from right to left  ` `static` `void` `rightToLeft( Node root, ``int` `level)  ` `{  ` `    ``if` `(root == ``null``)  ` `        ``return``;  ` ` `  `    ``if` `(level == ``1``)  ` `        ``System.out.print( root.data + ``" "``);  ` ` `  `    ``else` `if` `(level > ``1``)  ` `    ``{  ` `        ``rightToLeft(root.right, level - ``1``);  ` `        ``rightToLeft(root.left, level - ``1``);  ` `    ``}  ` `}  ` ` `  `// Function to print reverse clockwise spiral  ` `// traversal of a binary tree  ` `static` `void` `ReverseClockWiseSpiral( Node root)  ` `{  ` `    ``int` `i = ``1``;  ` `    ``int` `j = height(root);  ` ` `  `    ``// Flag to mark a change in the direction  ` `    ``// of printing nodes  ` `    ``int` `flag = ``0``;  ` `    ``while` `(i <= j)  ` `    ``{  ` ` `  `        ``// If flag is zero print nodes  ` `        ``// from right to left  ` `        ``if` `(flag == ``0``) ` `        ``{  ` `            ``rightToLeft(root, j);  ` ` `  `            ``// Set the value of flag as zero  ` `            ``// so that nodes are next time  ` `            ``// printed from left to right  ` `            ``flag = ``1``;  ` ` `  `            ``// Decrement j  ` `            ``j--;  ` `        ``}  ` ` `  `        ``// If flag is one print nodes  ` `        ``// from left to right  ` `        ``else`  `        ``{  ` `            ``leftToRight(root, i);  ` ` `  `            ``// Set the value of flag as zero  ` `            ``// so that nodes are next time  ` `            ``// printed from right to left  ` `            ``flag = ``0``;  ` ` `  `            ``// Increment i  ` `            ``i++;  ` `        ``}  ` `    ``}  ` `}  ` ` `  `// Driver code  ` `public` `static` `void` `main(String args[])  ` `{  ` `    ``Node root = ``new` `Node(``1``);  ` `    ``root.left = ``new` `Node(``2``);  ` `    ``root.right = ``new` `Node(``3``);  ` `    ``root.left.left = ``new` `Node(``4``);  ` `    ``root.right.left = ``new` `Node(``6``);  ` `    ``root.right.right = ``new` `Node(``7``);  ` `    ``root.left.right = ``new` `Node(``5``);  ` ` `  `    ``ReverseClockWiseSpiral(root);  ` `} ` `}  ` ` `  `// This code is contributed by Arnab Kundu `

## C#

 `// C# implementation of the approach  ` `using` `System; ` ` `  `class` `GFG ` `{ ` `     `  `// Binary tree node  ` `public` `class` `Node  ` `{  ` `    ``public` `Node left;  ` `    ``public` `Node right;  ` `    ``public` `int` `data;  ` ` `  `    ``public` `Node(``int` `data)  ` `    ``{  ` `        ``this``.data = data;  ` `        ``this``.left = ``null``;  ` `        ``this``.right = ``null``;  ` `    ``}  ` `};  ` ` `  `// Recursive Function to find height  ` `// of binary tree  ` `static` `int` `height( Node root)  ` `{  ` `    ``// Base condition  ` `    ``if` `(root == ``null``)  ` `        ``return` `0;  ` ` `  `    ``// Compute the height of each subtree  ` `    ``int` `lheight = height(root.left);  ` `    ``int` `rheight = height(root.right);  ` ` `  `    ``// Return the maximum of two  ` `    ``return` `Math.Max(1 + lheight, 1 + rheight);  ` `}  ` ` `  `// Function to Print Nodes from left to right  ` `static` `void` `leftToRight( Node root, ``int` `level)  ` `{  ` `    ``if` `(root == ``null``)  ` `        ``return``;  ` ` `  `    ``if` `(level == 1)  ` `        ``Console.Write( root.data + ``" "``);  ` ` `  `    ``else` `if` `(level > 1) ` `    ``{  ` `        ``leftToRight(root.left, level - 1);  ` `        ``leftToRight(root.right, level - 1);  ` `    ``}  ` `}  ` ` `  `// Function to Print Nodes from right to left  ` `static` `void` `rightToLeft( Node root, ``int` `level)  ` `{  ` `    ``if` `(root == ``null``)  ` `        ``return``;  ` ` `  `    ``if` `(level == 1)  ` `        ``Console.Write( root.data + ``" "``);  ` ` `  `    ``else` `if` `(level > 1)  ` `    ``{  ` `        ``rightToLeft(root.right, level - 1);  ` `        ``rightToLeft(root.left, level - 1);  ` `    ``}  ` `}  ` ` `  `// Function to print reverse clockwise spiral  ` `// traversal of a binary tree  ` `static` `void` `ReverseClockWiseSpiral( Node root)  ` `{  ` `    ``int` `i = 1;  ` `    ``int` `j = height(root);  ` ` `  `    ``// Flag to mark a change in the direction  ` `    ``// of printing nodes  ` `    ``int` `flag = 0;  ` `    ``while` `(i <= j)  ` `    ``{  ` ` `  `        ``// If flag is zero print nodes  ` `        ``// from right to left  ` `        ``if` `(flag == 0) ` `        ``{  ` `            ``rightToLeft(root, j);  ` ` `  `            ``// Set the value of flag as zero  ` `            ``// so that nodes are next time  ` `            ``// printed from left to right  ` `            ``flag = 1;  ` ` `  `            ``// Decrement j  ` `            ``j--;  ` `        ``}  ` ` `  `        ``// If flag is one print nodes  ` `        ``// from left to right  ` `        ``else` `        ``{  ` `            ``leftToRight(root, i);  ` ` `  `            ``// Set the value of flag as zero  ` `            ``// so that nodes are next time  ` `            ``// printed from right to left  ` `            ``flag = 0;  ` ` `  `            ``// Increment i  ` `            ``i++;  ` `        ``}  ` `    ``}  ` `}  ` ` `  `// Driver code  ` `public` `static` `void` `Main(String []args)  ` `{  ` `    ``Node root = ``new` `Node(1);  ` `    ``root.left = ``new` `Node(2);  ` `    ``root.right = ``new` `Node(3);  ` `    ``root.left.left = ``new` `Node(4);  ` `    ``root.right.left = ``new` `Node(6);  ` `    ``root.right.right = ``new` `Node(7);  ` `    ``root.left.right = ``new` `Node(5);  ` ` `  `    ``ReverseClockWiseSpiral(root);  ` `} ` `} ` ` `  `// This code contributed by Rajput-Ji `

Output:

```7 6 5 4 1 3 2
```

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