Given a Binary Tree, convert it to a Circular Doubly Linked List.
- The left and right pointers in nodes are to be used as previous and next pointers, respectively, in the converted Circular Linked List.
- The order of nodes in the List must be the same as in the order of the given Binary Tree.
- The first node of Inorder traversal must be the head node of the Circular List.
Example:
An in-place solution to this problem is discussed in the previous post.
In this post, a much simpler solution, but using extra O(n) space, is discussed.
In this approach, first, we do an In-Order traversal of the given binary tree, we store this traversal in a vector, which will be passed on to the function along with the tree. Now, generate a circular doubly linked list from the elements of the vector.
To generate a circular doubly linked list from the vector, make the first element of the vector as the head of the linked list and also create a current pointer that is right now pointing to the head. Now start traversing the array from the second element and do the following.
- Create a temporary pointer that points to the current pointer.
- Make a new node with the current element of the vector.
- Make the current right point to this new node.
- Make the current pointer the current right pointer.
- Now, finally, the current left point is a temporary pointer created in the first step.
Do this for all the elements and after the traversal is completed, make the current’s right (current is right now pointing to the last element of the vector) point to the head of the list and make the head’s left point to the current pointer. Finally, return the head.
Below is the implementation of the above approach:
C++
// A C++ program for conversion // of Binary Tree to CDLL #include <bits/stdc++.h> using namespace std; // A binary tree node has data, // and left and right pointers struct Node { int data; struct Node* left; struct Node* right; Node(int x) { data = x; left = right = NULL; } }; // Function to perform In-Order traversal of the // tree and store the nodes in a vector void inorder(Node* root, vector<int>& v) { if (!root) return; /* first recur on left child */ inorder(root->left, v); /* append the data of node in vector */ v.push_back(root->data); /* now recur on right child */ inorder(root->right, v); } // Function to convert Binary Tree to Circular // Doubly Linked list using the vector which stores // In-Order traversal of the Binary Tree Node* bTreeToCList(Node* root) { // Base cases if (root == NULL) return NULL; // Vector to be used for storing the nodes // of tree in In-order form vector<int> v; // Calling the In-Order traversal function inorder(root, v); // Create the head of the linked list pointing // to the root of the tree Node* head_ref = new Node(v[0]); // Create a current pointer to be used in traversal Node* curr = head_ref; // Traversing the nodes of the tree starting // from the second elements for (int i = 1; i < v.size(); i++) { // Create a temporary pointer // pointing to current Node* temp = curr; // Current's right points to the current // node in traversal curr->right = new Node(v[i]); // Current points to its right curr = curr->right; // Current's left points to temp curr->left = temp; } // Current's right points to head of the list curr->right = head_ref; // Head's left points to current head_ref->left = curr; // Return head of the list return head_ref; } // Display Circular Link List void displayCList(Node* head) { cout << "Circular Doubly Linked List is :\n"; Node* itr = head; do { cout << itr->data << " "; itr = itr->right; } while (head != itr); cout << "\n"; } // Driver Code int main() { Node* root = new Node(10); root->left = new Node(12); root->right = new Node(15); root->left->left = new Node(25); root->left->right = new Node(30); root->right->left = new Node(36); Node* head = bTreeToCList(root); displayCList(head); return 0; } |
Java
// Java program for conversion // of Binary Tree to CDLL import java.util.*; class GFG { // A binary tree node has data, // and left and right pointers static class Node { int data; Node left; Node right; Node(int x) { data = x; left = right = null; } }; // Function to perform In-Order traversal of the // tree and store the nodes in a vector static void inorder(Node root, Vector<Integer> v) { if (root == null) return; /* first recur on left child */ inorder(root.left, v); /* append the data of node in vector */ v.add(root.data); /* now recur on right child */ inorder(root.right, v); } // Function to convert Binary Tree to Circular // Doubly Linked list using the vector which stores // In-Order traversal of the Binary Tree static Node bTreeToCList(Node root) { // Base cases if (root == null) return null; // Vector to be used for storing the nodes // of tree in In-order form Vector<Integer> v = new Vector<>(); // Calling the In-Order traversal function inorder(root, v); // Create the head of the linked list pointing // to the root of the tree Node head_ref = new Node(v.get(0)); // Create a current pointer to be used in traversal Node curr = head_ref; // Traversing the nodes of the tree starting // from the second elements for (int i = 1; i < v.size(); i++) { // Create a temporary pointer // pointing to current Node temp = curr; // Current's right points to the current // node in traversal curr.right = new Node(v.get(i)); // Current points to its right curr = curr.right; // Current's left points to temp curr.left = temp; } // Current's right points to head of the list curr.right = head_ref; // Head's left points to current head_ref.left = curr; // Return head of the list return head_ref; } // Display Circular Link List static void displayCList(Node head) { System.out.println("Circular Doubly Linked List is :"); Node itr = head; do { System.out.print(itr.data + " "); itr = itr.right; } while (head != itr); System.out.println(); } // Driver Code public static void main(String[] args) { Node root = new Node(10); root.left = new Node(12); root.right = new Node(15); root.left.left = new Node(25); root.left.right = new Node(30); root.right.left = new Node(36); Node head = bTreeToCList(root); displayCList(head); } } // This code is contributed by Rajput-Ji |
Python
# Python program for conversion # of Binary Tree to CDLL # A binary tree node has data, # and left and right pointers class Node: def __init__(self, data): self.data = data self.left = self.right = None v = [] # Function to perform In-Order traversal of the # tree and store the nodes in a vector def inorder(root): global v if (root == None): return # first recur on left child inorder(root.left) # append the data of node in vector v.append(root.data) # now recur on right child inorder(root.right) # Function to convert Binary Tree to Circular # Doubly Linked list using the vector which stores # In-Order traversal of the Binary Tree def bTreeToCList(root): global v # Base cases if (root == None): return None # Vector to be used for storing the nodes # of tree in In-order form v = [] # Calling the In-Order traversal function inorder(root) # Create the head of the linked list pointing # to the root of the tree head_ref = Node(v[0]) # Create a current pointer to be used in traversal curr = head_ref i = 1 # Traversing the nodes of the tree starting # from the second elements while ( i < len(v)) : # Create a temporary pointer # pointing to current temp = curr # Current's right points to the current # node in traversal curr.right = Node(v[i]) # Current points to its right curr = curr.right # Current's left points to temp curr.left = temp i = i + 1 # Current's right points to head of the list curr.right = head_ref # Head's left points to current head_ref.left = curr # Return head of the list return head_ref # Display Circular Link List def displayCList(head): print("Circular Doubly Linked List is :", end = "") itr = head while(True): print(itr.data, end = " ") itr = itr.right if(head == itr): break print() # Driver Code root = Node(10) root.left = Node(12) root.right = Node(15) root.left.left = Node(25) root.left.right = Node(30) root.right.left = Node(36) head = bTreeToCList(root) displayCList(head) # This code is contributed by Arnab Kundu |
C#
// C# program for conversion // of Binary Tree to CDLL using System; using System.Collections.Generic; class GFG { // A binary tree node has data, // and left and right pointers public class Node { public int data; public Node left; public Node right; public Node(int x) { data = x; left = right = null; } }; // Function to perform In-Order traversal of the // tree and store the nodes in a vector static void inorder(Node root, List<int> v) { if (root == null) return; /* first recur on left child */ inorder(root.left, v); /* append the data of node in vector */ v.Add(root.data); /* now recur on right child */ inorder(root.right, v); } // Function to convert Binary Tree to Circular // Doubly Linked list using the vector which stores // In-Order traversal of the Binary Tree static Node bTreeToCList(Node root) { // Base cases if (root == null) return null; // Vector to be used for storing the nodes // of tree in In-order form List<int> v = new List<int>(); // Calling the In-Order traversal function inorder(root, v); // Create the head of the linked list // pointing to the root of the tree Node head_ref = new Node(v[0]); // Create a current pointer // to be used in traversal Node curr = head_ref; // Traversing the nodes of the tree starting // from the second elements for (int i = 1; i < v.Count; i++) { // Create a temporary pointer // pointing to current Node temp = curr; // Current's right points to the current // node in traversal curr.right = new Node(v[i]); // Current points to its right curr = curr.right; // Current's left points to temp curr.left = temp; } // Current's right points to head of the list curr.right = head_ref; // Head's left points to current head_ref.left = curr; // Return head of the list return head_ref; } // Display Circular Link List static void displayCList(Node head) { Console.WriteLine("Circular Doubly " + "Linked List is :"); Node itr = head; do { Console.Write(itr.data + " "); itr = itr.right; } while (head != itr); Console.WriteLine(); } // Driver Code public static void Main(String[] args) { Node root = new Node(10); root.left = new Node(12); root.right = new Node(15); root.left.left = new Node(25); root.left.right = new Node(30); root.right.left = new Node(36); Node head = bTreeToCList(root); displayCList(head); } } // This code is contributed by 29AjayKumar |
Javascript
<script> // javascript program for conversion // of Binary Tree to CDLL // A binary tree node has data, // and left and right pointers class Node { constructor(val) { this.data = val; this.left = null; this.right = null; } } // Function to perform In-Order traversal of the // tree and store the nodes in a vector function inorder(root, v) { if (root == null) return; /* first recur on left child */ inorder(root.left, v); /* append the data of node in vector */ v.push(root.data); /* now recur on right child */ inorder(root.right, v); } // Function to convert Binary Tree to Circular // Doubly Linked list using the vector which stores // In-Order traversal of the Binary Tree function bTreeToCList(root) { // Base cases if (root == null) return null; // Vector to be used for storing the nodes // of tree in In-order form var v = []; // Calling the In-Order traversal function inorder(root, v); // Create the head of the linked list pointing // to the root of the tree var head_ref = new Node(v[0]); // Create a current pointer to be used in traversal var curr = head_ref; // Traversing the nodes of the tree starting // from the second elements for (i = 1; i < v.length; i++) { // Create a temporary pointer // pointing to current var temp = curr; // Current's right points to the current // node in traversal curr.right = new Node(v[i]); // Current points to its right curr = curr.right; // Current's left points to temp curr.left = temp; } // Current's right points to head of the list curr.right = head_ref; // Head's left points to current head_ref.left = curr; // Return head of the list return head_ref; } // Display Circular Link List function displayCList(head) { document.write("Circular Doubly Linked List is :<br/>"); var itr = head; do { document.write(itr.data + " "); itr = itr.right; } while (head != itr); document.write(); } // Driver Code var root = new Node(10); root.left = new Node(12); root.right = new Node(15); root.left.left = new Node(25); root.left.right = new Node(30); root.right.left = new Node(36); var head = bTreeToCList(root); displayCList(head); // This code contributed by Rajput-Ji </script> |
Output:
Circular Doubly Linked List is : 25 12 30 10 36 15
Time Complexity: O(N), where N is the number of nodes in the Binary Tree.
Auxiliary Space: O(N)
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