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                <div class="alert alert-note">
  <h3>Binary Tree Traversal</h3>
    The process of visiting each node in the tree exactly once in some order. Visiting means reading/processing data in a node.</p>

    <strong>Breadth-First</strong> is also called as <strong>Level-Order</strong> traversal. We visit all of it's children before visiting it's grand children.

    <img src="" alt="Breadth-First">
    <strong> Depth-First </strong> we visit all the grand children before going to the siblings. The relative order of visiting left and right subtree can be different like <mark>in-order, pre-order and post-order.</mark> Visiting a child is visiting the complete subtree in that path.

    <img src="" alt="">
  <img src="">


                .alert {
  padding: 20px;
  border-radius: 25px;
  margin-bottom: 15px;

.alert-tip {
  background-color: #def6dd;

.alert-note {
  background-color: #efd9fd;
  overflow-x: auto;
pre {
  overflow-x: auto;
  white-space: pre-wrap;
  white-space: -moz-pre-wrap;
  white-space: -pre-wrap;
  white-space: -o-pre-wrap;
  word-wrap: break-word;



Nodes are created in the heap seciton of the memory 
Address of the root node we keep for a tree.

class Node {
  constructor(data) { = data;
    this.left = null;
    this.right = null;

O(n) time | O(n) space because we have queue.
Level-Order Traversal
function breadthFirst(root) {
  // Write your code here
  if (root == null) return;
  let queue = [root]; // O(n) space
  while (queue.length > 0) {
    let current = queue.shift(); // removing element at front.
    if (current.left) queue.push(current.left);
    if (current.right) queue.push(current.right);

let result = [];

function visit(node) {

// unit tests
// do not modify the below code
describe("Breadth First Traversal", () => {
  let root = null;

  beforeEach(() => {
    root = null;
    root = insert(root, 15);
    root = insert(root, 10);
    root = insert(root, 20);
    root = insert(root, 25);
    root = insert(root, 8);
    root = insert(root, 12);
  it("should work correctly", () => {
    expect(result).toEqual([15, 10, 20, 8, 12, 25]);

function insert(root, data) {
  // If the tree is empty create new node.
  let notToInsert = new Node(data);

  let current = root;
  let previous = null;
  while (current != null) {
    previous = current;
    if (data <= current = current.left;
    else current = current.right;

  if (previous == null) return notToInsert;
  else if (data <= previous.left = notToInsert;
  else previous.right = notToInsert;

  return root;