levelorderTraversal.cpp

// Recursive CPP program for level
// order traversal of Binary Tree
#include <bits/stdc++.h>
using namespace std;

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

/* Function prototypes */
void printCurrentLevel(node* root, int level);
int height(node* node);
node* newNode(int data);

/* Function to print level
order traversal a tree*/
void printLevelOrder(node* root)
{
	int h = height(root);
	int i;
	for (i = 1; i <= h; i++)
		printCurrentLevel(root, i);
}

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

	return 0;
}

// This code is contributed by rathbhupendra