level_order.c

#include <stdio.h>
#include <stdlib.h>

struct node {
	int data;
	struct node *left, *right;
};

void printCurrentLevel(struct node* root, int level);
int height(struct node* node);
struct node* newNode(int data);

void printLevelOrder(struct node* root)
{
	int h = height(root);
	int i;
	for (i = 1; i <= h; i++)
		printCurrentLevel(root, i);
}

void printCurrentLevel(struct node* root, int level)
{
	if (root == NULL)
		return;
	if (level == 1)
		printf("%d ", root->data);
	else if (level > 1) {
		printCurrentLevel(root->left, level - 1);
		printCurrentLevel(root->right, level - 1);
	}
}

int height(struct 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);
	}
}

struct node* newNode(int data)
{
	struct node* node
		= (struct node*)malloc(sizeof(struct node));
	node->data = data;
	node->left = NULL;
	node->right = NULL;

	return (node);
}

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

	printf("Level Order traversal of binary tree is \n");
	printLevelOrder(root);

	return 0;
}