Given a Binary Tree, convert it to a Circular Doubly Linked List (In-Place).
- The left and right pointers in nodes are to be used as previous and next pointers respectively in converted Circular Linked List.
- The order of nodes in List must be same as Inorder of the given Binary Tree.
- The first node of Inorder traversal must be head node of the Circular List.
Example:
The idea can be described using below steps.
1) Write a general purpose function that concatenates two given circular doubly lists (This function is explained below).
2) Now traverse the given tree
….a) Recursively convert left subtree to a circular DLL. Let the converted list be leftList.
….a) Recursively convert right subtree to a circular DLL. Let the converted list be rightList.
….c) Make a circular linked list of root of the tree, make left and right of root to point to itself.
….d) Concatenate leftList with list of single root node.
….e) Concatenate the list produced in step above (d) with rightList.
Note that the above code traverses tree in Postorder fashion. We can traverse in inorder fashion also. We can first concatenate left subtree and root, then recur for right subtree and concatenate the result with left-root concatenation.
How to Concatenate two circular DLLs?
- Get the last node of the left list. Retrieving the last node is an O(1) operation, since the prev pointer of the head points to the last node of the list.
- Connect it with the first node of the right list
- Get the last node of the second list
- Connect it with the head of the list.
Below are implementations of above idea.
C++
// C++ Program to convert a Binary Tree // to a Circular Doubly Linked List #include<iostream> using namespace std; // To represents a node of a Binary Tree struct Node { struct Node *left, *right; int data; }; // A function that appends rightList at the end // of leftList. Node *concatenate(Node *leftList, Node *rightList) { // If either of the list is empty // then return the other list if (leftList == NULL) return rightList; if (rightList == NULL) return leftList; // Store the last Node of left List Node *leftLast = leftList->left; // Store the last Node of right List Node *rightLast = rightList->left; // Connect the last node of Left List // with the first Node of the right List leftLast->right = rightList; rightList->left = leftLast; // Left of first node points to // the last node in the list leftList->left = rightLast; // Right of last node refers to the first // node of the List rightLast->right = leftList; return leftList; } // Function converts a tree to a circular Linked List // and then returns the head of the Linked List Node *bTreeToCList(Node *root) { if (root == NULL) return NULL; // Recursively convert left and right subtrees Node *left = bTreeToCList(root->left); Node *right = bTreeToCList(root->right); // Make a circular linked list of single node // (or root). To do so, make the right and // left pointers of this node point to itself root->left = root->right = root; // Step 1 (concatenate the left list with the list // with single node, i.e., current node) // Step 2 (concatenate the returned list with the // right List) return concatenate(concatenate(left, root), right); } // Display Circular Link List void displayCList(Node *head) { cout << "Circular Linked List is :
"; Node *itr = head; do { cout << itr->data <<" "; itr = itr->right; } while (head!=itr); cout << "
"; } // Create a new Node and return its address Node *newNode(int data) { Node *temp = new Node(); temp->data = data; temp->left = temp->right = NULL; return temp; } // Driver Program to test above function int main() { Node *root = newNode(10); root->left = newNode(12); root->right = newNode(15); root->left->left = newNode(25); root->left->right = newNode(30); root->right->left = newNode(36); Node *head = bTreeToCList(root); displayCList(head); return 0; } |
Java
// Java Program to convert a Binary Tree to a // Circular Doubly Linked List // Node class represents a Node of a Tree class Node { int val; Node left,right; public Node(int val) { this.val = val; left = right = null; } } // A class to represent a tree class Tree { Node root; public Tree() { root = null; } // concatenate both the lists and returns the head // of the List public Node concatenate(Node leftList,Node rightList) { // If either of the list is empty, then // return the other list if (leftList == null) return rightList; if (rightList == null) return leftList; // Store the last Node of left List Node leftLast = leftList.left; // Store the last Node of right List Node rightLast = rightList.left; // Connect the last node of Left List // with the first Node of the right List leftLast.right = rightList; rightList.left = leftLast; // left of first node refers to // the last node in the list leftList.left = rightLast; // Right of last node refers to the first // node of the List rightLast.right = leftList; // Return the Head of the List return leftList; } // Method converts a tree to a circular // Link List and then returns the head // of the Link List public Node bTreeToCList(Node root) { if (root == null) return null; // Recursively convert left and right subtrees Node left = bTreeToCList(root.left); Node right = bTreeToCList(root.right); // Make a circular linked list of single node // (or root). To do so, make the right and // left pointers of this node point to itself root.left = root.right = root; // Step 1 (concatenate the left list with the list // with single node, i.e., current node) // Step 2 (concatenate the returned list with the // right List) return concatenate(concatenate(left, root), right); } // Display Circular Link List public void display(Node head) { System.out.println("Circular Linked List is :"); Node itr = head; do { System.out.print(itr.val+ " " ); itr = itr.right; } while (itr != head); System.out.println(); } } // Driver Code class Main { public static void main(String args[]) { // Build the tree Tree tree = new Tree(); tree.root = new Node(10); tree.root.left = new Node(12); tree.root.right = new Node(15); tree.root.left.left = new Node(25); tree.root.left.right = new Node(30); tree.root.right.left = new Node(36); // head refers to the head of the Link List Node head = tree.bTreeToCList(tree.root); // Display the Circular LinkedList tree.display(head); } } |
Python3
# Python3 Program to convert a Binary # Tree to a Circular Doubly Linked List class newNode: def __init__(self, data): self.data = data self.left = self.right = None # A function that appends rightList # at the end of leftList. def concatenate(leftList, rightList): # If either of the list is empty # then return the other list if (leftList == None): return rightList if (rightList == None): return leftList # Store the last Node of left List leftLast = leftList.left # Store the last Node of right List rightLast = rightList.left # Connect the last node of Left List # with the first Node of the right List leftLast.right = rightList rightList.left = leftLast # Left of first node points to # the last node in the list leftList.left = rightLast # Right of last node refers to # the first node of the List rightLast.right = leftList return leftList # Function converts a tree to a circular # Linked List and then returns the head # of the Linked List def bTreeToCList(root): if (root == None): return None # Recursively convert left and # right subtrees left = bTreeToCList(root.left) right = bTreeToCList(root.right) # Make a circular linked list of single # node (or root). To do so, make the # right and left pointers of this node # point to itself root.left = root.right = root # Step 1 (concatenate the left list # with the list with single # node, i.e., current node) # Step 2 (concatenate the returned list # with the right List) return concatenate(concatenate(left, root), right) # Display Circular Link List def displayCList(head): print("Circular Linked List is :") itr = head first = 1 while (head != itr or first): print(itr.data, end = " ") itr = itr.right first = 0 print() # Driver Code if __name__ == '__main__': root = newNode(10) root.left = newNode(12) root.right = newNode(15) root.left.left = newNode(25) root.left.right = newNode(30) root.right.left = newNode(36) head = bTreeToCList(root) displayCList(head) # This code is contributed by PranchalK |
C#
// C# Program to convert a Binary Tree // to a Circular Doubly Linked List using System; // Node class represents a Node of a Tree public class Node { public int val; public Node left, right; public Node(int val) { this.val = val; left = right = null; } } // A class to represent a tree public class Tree { internal Node root; public Tree() { root = null; } // concatenate both the lists // and returns the head of the List public virtual Node concatenate(Node leftList, Node rightList) { // If either of the list is empty, // then return the other list if (leftList == null) { return rightList; } if (rightList == null) { return leftList; } // Store the last Node of left List Node leftLast = leftList.left; // Store the last Node of right List Node rightLast = rightList.left; // Connect the last node of Left List // with the first Node of the right List leftLast.right = rightList; rightList.left = leftLast; // left of first node refers to // the last node in the list leftList.left = rightLast; // Right of last node refers to // the first node of the List rightLast.right = leftList; // Return the Head of the List return leftList; } // Method converts a tree to a circular // Link List and then returns the head // of the Link List public virtual Node bTreeToCList(Node root) { if (root == null) { return null; } // Recursively convert left // and right subtrees Node left = bTreeToCList(root.left); Node right = bTreeToCList(root.right); // Make a circular linked list of single // node (or root). To do so, make the // right and left pointers of this node // point to itself root.left = root.right = root; // Step 1 (concatenate the left list with // the list with single node, // i.e., current node) // Step 2 (concatenate the returned list // with the right List) return concatenate(concatenate(left, root), right); } // Display Circular Link List public virtual void display(Node head) { Console.WriteLine("Circular Linked List is :"); Node itr = head; do { Console.Write(itr.val + " "); itr = itr.right; } while (itr != head); Console.WriteLine(); } } // Driver Code public class GFG { public static void Main(string[] args) { // Build the tree Tree tree = new Tree(); tree.root = new Node(10); tree.root.left = new Node(12); tree.root.right = new Node(15); tree.root.left.left = new Node(25); tree.root.left.right = new Node(30); tree.root.right.left = new Node(36); // head refers to the head of the Link List Node head = tree.bTreeToCList(tree.root); // Display the Circular LinkedList tree.display(head); } } // This code is contributed by Shrikant13 |
Output:
Circular Linked List is : 25 12 30 10 36 15
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