Find top three elements of binary tree in c++

C++ program for Find top three elements of binary tree. Here mentioned other language solution.

// Include header file
#include <iostream>
using namespace std;
/*
  C++ program for
  Find top three elements in binary tree
*/
// Node of Binary Tree
class TreeNode
{
	public: 
    int data;
	TreeNode *left;
	TreeNode *right;
	TreeNode(int data)
	{
		//Set node value
		this->data = data;
		this->left = nullptr;
		this->right = nullptr;
	}
};
class BinaryTree
{
	public: 
    TreeNode *root;
	TreeNode *first;
	TreeNode *second;
	TreeNode *third;
	BinaryTree()
	{
		this->root = nullptr;
		this->first = nullptr;
		this->second = nullptr;
		this->third = nullptr;
	}
	// Recursive function
	// Display preorder view of binary tree
	void preOrder(TreeNode *node)
	{
		if (node != nullptr)
		{
			//Print node value
			cout << "  " << node->data;
			this->preOrder(node->left);
			this->preOrder(node->right);
		}
	}
	// Find top three largest nodes in binary tree
	void getTopThree(TreeNode *node)
	{
		if (node != nullptr)
		{
			if (this->first == nullptr)
			{
				// First node of tree
				this->first = node;
			}
			else if (this->first->data < node->data)
			{
				// When get new first largest node
				// Interchange the node values
				this->third = this->second;
				this->second = this->first;
				this->first = node;
			}
			else if (this->second == nullptr)
			{
				if (this->first->data != node->data)
				{
					// Get second largest node
					this->second = node;
				}
			}
			else
			{
				if (this->second->data < node->data && 
                    this->first->data > node->data)
				{
					// When we get new second largest
					// Replace the third node with the second node
					this->third = this->second;
					// This is new second largest element
					this->second = node;
				}
				else if (this->third == nullptr)
				{
					if (this->second->data > node->data && 
                        this->first->data > node->data)
					{
						// Get the third largest node
						this->third = node;
					}
				}
				else if (this->third->data < node->data && 
                         this->first->data > node->data && 
                         this->second->data > node->data)
				{
					this->third = node;
				}
			}
			// Recursively, execute left and right subtree
			this->getTopThree(node->left);
			this->getTopThree(node->right);
		}
	}
	// This are handle the request to finding 
	// top three nodes in binary tree.
	void printTopThree()
	{
		if (this->root == nullptr)
		{
			return;
		}
		// Display tree elements
		cout << "\n Preorder : ";
		this->preOrder(this->root);
		// Set the initial all three nodes
		this->first = nullptr;
		this->second = nullptr;
		this->third = nullptr;
		// Find three largest element
		this->getTopThree(this->root);
		// Display calculated result
		cout << "\n First : " << this->first->data << endl;
		if (this->second != nullptr && 
            this->second != this->first && 
            this->second->data < this->first->data)
		{
			cout << " Second : " << this->second->data << endl;
		}
		else
		{
			cout << " Second : None " << endl;
		}
		if (this->third != nullptr && 
            this->third != this->second && 
            this->third != this->first && 
            this->third->data < this->second->data)
		{
			cout << " Third : " << this->third->data << endl;
		}
		else
		{
			cout << " Third : None" << endl;
		}
	}
};
int main()
{
	// Create two trees
	BinaryTree *x = new BinaryTree();
	BinaryTree *y = new BinaryTree();
	/*
	    Construct Binary Tree
	    -----------------------
	           10
	          /  \
	         /    \
	        6      8
	       / \    / \
	      12  3  7   5
	     /        \   \
	    9         -6  13
	*/
	// Add nodes
	x->root = new TreeNode(10);
	x->root->left = new TreeNode(6);
	x->root->left->left = new TreeNode(12);
	x->root->right = new TreeNode(8);
	x->root->right->right = new TreeNode(5);
	x->root->right->left = new TreeNode(7);
	x->root->right->left->right = new TreeNode(-6);
	x->root->left->right = new TreeNode(3);
	x->root->left->left->left = new TreeNode(9);
	x->root->right->right->right = new TreeNode(13);
	/* 
	    Construct Tree
	    --------------
	         1
	        / \ 
	       /   \
	      1     2
	     /     / \
	    1     2   2
	*/
	// Add second tree node
	y->root = new TreeNode(1);
	y->root->left = new TreeNode(1);
	y->root->right = new TreeNode(2);
	y->root->right->right = new TreeNode(2);
	y->root->right->left = new TreeNode(2);
	y->root->left->left = new TreeNode(1);
	// Test One
	x->printTopThree();
	// Test Two
	y->printTopThree();
	return 0;
}

Output

 Preorder :   10  6  12  9  3  8  7  -6  5  13
 First : 13
 Second : 12
 Third : 10

 Preorder :   1  1  1  2  2  2
 First : 2
 Second : 1
 Third : None