Hello! So I’m doing a 100 day coding challenge where I solve a few questions every day and thought of posting them here on my blog so that you guys can join the challenge too!
Welcome to Coding challenge Day 13: Problem 1! Be sure to post your answers, queries etc in the comments!
Problem: Level-order traversal of a Binary tree
Sample:

Output:
Level: 0
1
Level: 1
2
3
Level: 2
4
5
6
7
Level: 3
Solution:
package tree.binarytree;
import java.util.Queue;
import java.util.LinkedList;
public class Program011level_order_traversal {
static class Node{
int data;
Node left, right;
public Node(int d){
data=d;
left=right=null;
}
}
static class Binary_tree{
Node root;
public Binary_tree(){
root=null;
}
public void add_left (Node parent_node, Node node){
parent_node.left= node;
}
public void add_right (Node parent_node, Node node){
parent_node.right= node;
}
public void level_order_traversal(){
Node node= root;
Node level_node= new Node(-1);
Node previous_node= root;
int level=0;
Queue<Node> queue= new LinkedList<Node>();
queue.add(root);
queue.add(level_node);
System.out.println("Level: 0");
while(!queue.isEmpty()){
Node front_node= queue.poll();
if(front_node.data==-1){
level++;
if(previous_node.data!=-1){
queue.add(level_node);
System.out.println("Level: " + level);
}
} else{
System.out.println(front_node.data);
if(front_node.left!=null){
queue.add(front_node.left);
}
if(front_node.right!=null){
queue.add(front_node.right);
}
}
previous_node= front_node;
}
}
}
public static void main (String [] args){
Binary_tree tree= new Binary_tree();
tree.root= new Node(1);
Node node2= new Node(2);
tree.add_left(tree.root, node2);
Node node3= new Node(3);
tree.add_right(tree.root, node3);
Node node4= new Node (4);
tree.add_left(node2, node4);
Node node5= new Node(5);
tree.add_right(node2, node5);
Node node6= new Node(6);
tree.add_left(node3, node6);
Node node7= new Node(7);
tree.add_right(node3, node7);
tree.level_order_traversal();
}
}
Happy Learning!!