Level Order Tree Traversal in Data Structures

In this section we will see the level-order traversal technique for binary search tree.

Suppose we have one tree like this −

The traversal sequence will be like: 10, 5, 16, 8, 15, 20, 23


   define queue que to store nodes
   insert root into the que.
   while que is not empty, do
      item := item present at front position of queue
      print the value of item
      if left of the item is not null, then
         insert left of item into que
      end if
      if right of the item is not null, then
         insert right of item into que
      end if
      delete front element from que


 Live Demo

using namespace std;
class node{
      int h_left, h_right, bf, value;
      node *left, *right;
class tree{
      node *get_node(int key);
      node *root;
         root = NULL; //set root as NULL at the beginning
      void levelorder_traversal(node *r);
      node *insert_node(node *root, int key);
node *tree::get_node(int key){
   node *new_node;
   new_node = new node; //create a new node dynamically
   new_node->h_left = 0; new_node->h_right = 0;
   new_node->bf = 0;
   new_node->value = key; //store the value from given key
   new_node->left = NULL; new_node->right = NULL;
   return new_node;
void tree::levelorder_traversal(node *root){
   queue <node*> que;
   node *item;
   que.push(root); //insert the root at first
      item = que.front(); //get the element from the front end
      cout << item->value << " ";
      if(item->left != NULL) //When left child is present, insert into queue
      if(item->right != NULL) //When right child is present, insert into queue
      que.pop(); //remove the item from queue
node *tree::insert_node(node *root, int key){
   if(root == NULL){
      return (get_node(key)); //when tree is empty, create a node as root
   if(key < root->value){ //when key is smaller than root value, go to the left
      root->left = insert_node(root->left, key);
   } else if(key > root->value) { //when key is greater than root value, go to the right
      root->right = insert_node(root->right, key);
   return root; //when key is already present, do not insert it again
   node *root;
   tree my_tree;
   //Insert some keys into the tree.
   my_tree.root = my_tree.insert_node(my_tree.root, 10);
   my_tree.root = my_tree.insert_node(my_tree.root, 5);
   my_tree.root = my_tree.insert_node(my_tree.root, 16);
   my_tree.root = my_tree.insert_node(my_tree.root, 20);
   my_tree.root = my_tree.insert_node(my_tree.root, 15);
   my_tree.root = my_tree.insert_node(my_tree.root, 8);
   my_tree.root = my_tree.insert_node(my_tree.root, 23);
   cout << "Level-Order Traversal: ";


Level-Order Traversal: 10 5 16 8 15 20 23

Updated on: 27-Aug-2019


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