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

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++

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// C++ implementation of the approach
#include <bits/stdc++.h>
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;
}

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Java

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// 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

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C#

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// 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

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Output:

7 6 5 4 1 3 2    


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