Untitled

import java.util.LinkedList;
import java.util.Queue;

public class App {

  

    static void levelOrderTraversal(TreeNode root){
        if(root == null) return;

        Queue<TreeNode> myQueue = new LinkedList<>();
        myQueue.add(root);
        // sebagai penanda tanda ganti level
        myQueue.add(null);
        
// selama queue tidak kosong, pop queue
        while(!myQueue.isEmpty()){
            TreeNode current = myQueue.poll();

            // jika elemen null padahal tree tidak kosong, artinya level berakhir
            if(current==null){
                if(!myQueue.isEmpty()){
                     // sebagai penanda tanda ganti level
                    myQueue.add(null);
                }
            }else {
                // push anak kiri dahulu sebelum anak kanan
                if (current.leftChild != null)
                  myQueue.add(current.leftChild);
         
               
                if (current.rightChild != null)
                  myQueue.add(current.rightChild);
         
                System.out.print(current.data + " ");
              }
        }

    }


    public static void main(String[] args) throws Exception {
        TreeNode root = new TreeNode(1);
        root.leftChild = new TreeNode(2);
        root.rightChild = new TreeNode(3);
        root.leftChild.leftChild = new TreeNode(4);
        root.leftChild.rightChild = new TreeNode(5);
        root.rightChild.leftChild = new TreeNode(6);
        root.rightChild.rightChild = new TreeNode(7);
        root.leftChild.leftChild.leftChild = new TreeNode(8);
        root.leftChild.leftChild.rightChild = new TreeNode(9);
        root.leftChild.rightChild.leftChild = new TreeNode(10);
        root.leftChild.rightChild.rightChild = new TreeNode(11);

        levelOrderTraversal(root);
         }
}


class TreeNode{
    int data;
    TreeNode leftChild;
    TreeNode rightChild;

    TreeNode(int data){
        this.data=data;
        leftChild = null;
        rightChild = null;
    }
}