Create Complete_Binary_Tree_from_Linked_List.cpp

Complete_Binary_Tree_from_Linked_List.cpp

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+// C++ program to create a Complete Binary tree from its Linked List
+// Representation
+#include <iostream>
+#include <string>
+#include <queue>
+using namespace std;
+
+// Linked list node
+struct ListNode
+{
+	int data;
+	ListNode* next;
+};
+
+// Binary tree node structure
+struct BinaryTreeNode
+{
+	int data;
+	BinaryTreeNode *left, *right;
+};
+
+// Function to insert a node at the beginning of the Linked List
+void push(struct ListNode** head_ref, int new_data)
+{
+	// allocate node and assign data
+	struct ListNode* new_node = new ListNode;
+	new_node->data = new_data;
+
+	// link the old list off the new node
+	new_node->next = (*head_ref);
+
+	// move the head to point to the new node
+	(*head_ref) = new_node;
+}
+
+// method to create a new binary tree node from the given data
+BinaryTreeNode* newBinaryTreeNode(int data)
+{
+	BinaryTreeNode *temp = new BinaryTreeNode;
+	temp->data = data;
+	temp->left = temp->right = NULL;
+	return temp;
+}
+
+// converts a given linked list representing a complete binary tree into the
+// linked representation of binary tree.
+void convertList2Binary(ListNode *head, BinaryTreeNode* &root)
+{
+	// queue to store the parent nodes
+	queue<BinaryTreeNode *> q;
+
+	// Base Case
+	if (head == NULL)
+	{
+		root = NULL; // Note that root is passed by reference
+		return;
+	}
+
+	// 1.) The first node is always the root node, and add it to the queue
+	root = newBinaryTreeNode(head->data);
+	q.push(root);
+
+	// advance the pointer to the next node
+	head = head->next;
+
+	// until the end of linked list is reached, do the following steps
+	while (head)
+	{
+		// 2.a) take the parent node from the q and remove it from q
+		BinaryTreeNode* parent = q.front();
+		q.pop();
+
+		// 2.c) take next two nodes from the linked list. We will add
+		// them as children of the current parent node in step 2.b. Push them
+		// into the queue so that they will be parents to the future nodes
+		BinaryTreeNode *leftChild = NULL, *rightChild = NULL;
+		leftChild = newBinaryTreeNode(head->data);
+		q.push(leftChild);
+		head = head->next;
+		if (head)
+		{
+			rightChild = newBinaryTreeNode(head->data);
+			q.push(rightChild);
+			head = head->next;
+		}
+
+		// 2.b) assign the left and right children of parent
+		parent->left = leftChild;
+		parent->right = rightChild;
+
+
+	}
+}
+
+// Utility function to traverse the binary tree after conversion
+void inorderTraversal(BinaryTreeNode* root)
+{
+	if (root)
+	{
+		inorderTraversal( root->left );
+		cout << root->data << " ";
+		inorderTraversal( root->right );
+	}
+}
+
+// Driver program to test above functions
+int main()
+{
+	// create a linked list shown in above diagram
+	struct ListNode* head = NULL;
+	push(&head, 36); /* Last node of Linked List */
+	push(&head, 30);
+	push(&head, 25);
+	push(&head, 15);
+	push(&head, 12);
+	push(&head, 10); /* First node of Linked List */
+
+	BinaryTreeNode *root;
+	convertList2Binary(head, root);
+
+	cout << "Inorder Traversal of the constructed Binary Tree is: \n";
+	inorderTraversal(root);
+	return 0;
+}