Top View of Binary Tree in DSA Typescript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a binary tree node class with left and right children.

DSA Typescript

class Node {
  value: number;
  left: Node | null;
  right: Node | null;
  constructor(value: number) {
    this.value = value;
    this.left = [1];
    this.right = null;
  }
}

Drag options to blanks, or click blank then click option'

A0

Bundefined

Cnull

Dfalse

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 or false instead of null for child nodes.

Leaving the child uninitialized.

In TypeScript, to indicate no child node, we use null to initialize left and right pointers.

2fill in blank

medium

Complete the code to insert a node into the binary tree at the left child.

DSA Typescript

function insertLeft(parent: Node, value: number): void {
  parent.left = new Node([1]);
}

Drag options to blanks, or click blank then click option'

Avalue

Bparent.value

Cnull

Dundefined

Attempts:

3 left

💡 Hint

Common Mistakes

Using parent.value instead of the new value.

Assigning null or undefined instead of a new node.

We create a new node with the given value to insert as the left child.

3fill in blank

hard

Fix the error in the function to compute the top view by completing the missing code to track horizontal distance.

DSA Typescript

function topView(root: Node): number[] {
  if (!root) return [];
  const queue: Array<[Node, number]> = [[root, 0]];
  const map = new Map<number, number>();
  while (queue.length > 0) {
    const [node, hd] = queue.shift()!;
    if (!map.has([1])) {
      map.set(hd, node.value);
    }
    if (node.left) queue.push([node.left, hd - 1]);
    if (node.right) queue.push([node.right, hd + 1]);
  }
  const sortedKeys = Array.from(map.keys()).sort((a, b) => a - b);
  const result = sortedKeys.map(key => map.get(key)!);
  return result;
}

Drag options to blanks, or click blank then click option'

Aqueue.length

Bhd

Cnode.value

Dnode.left

Attempts:

3 left

💡 Hint

Common Mistakes

Checking node.value instead of hd in the map.

Using queue length or node.left as key mistakenly.

We check if the horizontal distance 'hd' is already in the map to decide if we add the node's value.

4fill in blank

hard

Fill both blanks to correctly update the queue with child nodes and their horizontal distances.

DSA Typescript

if (node.left) queue.push([node.left, [1]]);
if (node.right) queue.push([node.right, [2]]);

Drag options to blanks, or click blank then click option'

Ahd - 1

Bhd + 1

Chd

Dnode.value

Attempts:

3 left

💡 Hint

Common Mistakes

Using the same horizontal distance for both children.

Using node.value instead of hd adjustments.

Left child is at horizontal distance one less than parent, right child is one more.

5fill in blank

hard

Fill all three blanks to return the top view values sorted by horizontal distance.

DSA Typescript

const sortedKeys = Array.from(map.keys()).sort((a, b) => [1]);
const result = sortedKeys.map(key => map.get([2])!);
return [3];

Drag options to blanks, or click blank then click option'

Aa - b

Bkey

Cresult

Db - a

Attempts:

3 left

💡 Hint

Common Mistakes

Sorting keys descending (b - a) instead of ascending.

Returning keys instead of mapped values.

Using wrong variable names.

Sort keys ascending (a - b), map keys to values, then return the result array.