How do you implement a binary tree using a linked list?

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#include <iostream>

#include <queue>

using namespace std;

// A Binary Tree Node

struct TreeNode

{

int data;

TreeNode *left, *right;

TreeNode(int data)

{

this->data = data;

this->left = this->right = nullptr;

}

};

// A Linked List Node

struct ListNode

{

int data;

ListNode* next;

ListNode(int data)

{

this->data = data;

this->next = nullptr;

}

};

// Utility function to create a new node with the given data and

// pushes it onto the list's front

ListNode* push(ListNode* head, int data)

{

ListNode* node = new ListNode(data);

node->next = head;

head = node;

return head;

}

// Function to perform preorder traversal on a given binary tree.

void preorder(TreeNode* root)

{

if (root == nullptr) {

return;

}

cout << root->data << ' ';

preorder(root->left);

preorder(root->right);

}

// Function to construct a complete binary tree from a given linked list

TreeNode* convertListToBinaryTree(ListNode* head)

{

// base case

if (head == nullptr) {

return nullptr;

}

// create the root using the first node of the linked list

TreeNode* root = new TreeNode(head->data);

// move the head pointer to the next node

head = head->next;

// create a queue to store tree pointers and enqueue the root node

queue<TreeNode*> q;

q.push(root);

// loop till the end of the linked list is reached

while (head)

{

// dequeue front node

TreeNode* front = q.front();

q.pop();

// create a left child from the next node in the linked list and enqueue it

front->left = new TreeNode(head->data);

q.push(front->left);

// move the head pointer to the next node

head = head->next;

// if the linked list did not reach its end

if (head != nullptr)

{

// create the right child from the next node in the linked list and

// enqueue it

front->right = new TreeNode(head->data);

q.push(front->right);

// move the head pointer to the next node

head = head->next;

}

}

// return root of the constructed binary tree

return root;

}

int main()

{

ListNode* head = nullptr;

int n = 6;

// construct a linked list

for (int i = n; i > 0; i--) {

head = push(head, i);

}

TreeNode* root = convertListToBinaryTree(head);

preorder(root);

return 0;

}