Reverse.cpp

#https://twitter.com/rohit17997637/status/1311534857688813569
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// A recursive C++ program to print 
// REVERSE level order traversal 
#include <bits/stdc++.h>
using namespace std;

/* A binary tree node has data, 
pointer to left and right child */
class node 
{ 
	public:
	int data; 
	node* left; 
	node* right; 
}; 

/*Function protoypes*/
void printGivenLevel(node* root, int level); 
int height(node* node); 
node* newNode(int data); 

/* Function to print REVERSE 
level order traversal a tree*/
void reverseLevelOrder(node* root) 
{ 
	int h = height(root); 
	int i; 
	for (i=h; i>=1; i--) //THE ONLY LINE DIFFERENT FROM NORMAL LEVEL ORDER 
		printGivenLevel(root, i); 
} 

/* Print nodes at a given level */
void printGivenLevel(node* root, int level) 
{ 
	if (root == NULL) 
		return; 
	if (level == 1) 
		cout << root->data << " "; 
	else if (level > 1) 
	{ 
		printGivenLevel(root->left, level - 1); 
		printGivenLevel(root->right, level - 1); 
	} 
} 

/* Compute the "height" of a tree -- the number of 
	nodes along the longest path from the root node 
	down to the farthest leaf node.*/
int height(node* node) 
{ 
	if (node == NULL) 
		return 0; 
	else
	{ 
		/* compute the height of each subtree */
		int lheight = height(node->left); 
		int rheight = height(node->right); 

		/* use the larger one */
		if (lheight > rheight) 
			return(lheight + 1); 
		else return(rheight + 1); 
	} 
} 

/* Helper function that allocates a new node with the 
given data and NULL left and right pointers. */
node* newNode(int data) 
{ 
	node* Node = new node();
	Node->data = data; 
	Node->left = NULL; 
	Node->right = NULL; 

	return(Node); 
} 

/* Driver code*/
int main() 
{ 
	node *root = newNode(1); 
	root->left = newNode(2); 
	root->right = newNode(3); 
	root->left->left = newNode(4); 
	root->left->right = newNode(5); 

	cout << "Level Order traversal of binary tree is \n"; 
	reverseLevelOrder(root); 

	return 0; 

} 

// This code is contributed by rathbhupendra