Why Trees Exist and What Linked Lists and Arrays Cannot Do in DSA Typescript - Test Your Knowledge

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a tree node with a value and empty children array.

DSA Typescript

class TreeNode {
  value: number;
  children: TreeNode[];
  constructor(val: number) {
    this.value = val;
    this.children = [1];
  }
}

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

A[]

B{}

Cnull

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using {} which creates an object instead of an array.

Setting children to null or 0 which are not arrays.

The children property should be an empty array to hold child nodes.

2fill in blank

medium

Complete the code to add a child node to a tree node's children array.

DSA Typescript

function addChild(parent: TreeNode, child: TreeNode) {
  parent.children.[1](child);
}

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

Ashift

Bpush

Cpop

Dunshift

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop() which removes the last element instead of adding.

Using shift() or unshift() which affect the start of the array.

Use push() to add a new child node at the end of the children array.

3fill in blank

hard

Fix the error in the code to check if a node has children.

DSA Typescript

function hasChildren(node: TreeNode): boolean {
  return node.children.length [1] 0;
}

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

A==

B!=

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using == 0 which checks for no children.

Using != 0 which is less clear than > 0.

We check if the children array length is greater than 0 to know if there are children.

4fill in blank

hard

Fill both blanks to create a function that counts total nodes in a tree recursively.

DSA Typescript

function countNodes(node: TreeNode): number {
  let count = 1;
  for (const child of node.children) {
    count += countNodes([1]);
  }
  return count;
}

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

Anode

Bcount

Cchildren

Dchild

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'node' which causes infinite recursion on the same node.

Using 'children' which is an array, not a node.

We recursively count nodes by calling countNodes on each child node.

5fill in blank

hard

Fill all three blanks to create a function that finds a node by value in a tree.

DSA Typescript

function findNode(node: TreeNode, val: number): TreeNode | null {
  if (node.value === [1]) return node;
  for (const child of node.[2]) {
    const found = findNode(child, [3]);
    if (found) return found;
  }
  return null;
}

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

Aval

Bchildren

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'value' instead of 'val' in comparisons.

Looping over 'value' instead of 'children'.

Passing wrong variable in recursive call.

We compare node.value to val, loop over children, and pass val recursively.