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

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a root node for a tree.

DSA Javascript

const root = { value: 10, children: [1] };

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

Anull

B{}

C[]

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using {} which is an object, not a list.

Using null which means no children but we want an empty list.

Using 0 which is a number, not a list.

The children of a tree node are stored in an array to hold multiple child nodes.

2fill in blank

medium

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

DSA Javascript

root.children.[1]({ value: 20, children: [] });

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

Apush

Bunshift

Cshift

Dpop

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop which removes the last element.

Using shift which removes the first element.

Using unshift which adds to the start, not the end.

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

3fill in blank

hard

Fix the error in the function that counts total nodes in a tree.

DSA Javascript

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

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

Achild

Bnode

Cchildren

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Passing node causes infinite recursion.

Passing children is undefined in this scope.

Passing count is a number, not a node.

We must recursively count nodes starting from each child node, so pass child to the recursive call.

4fill in blank

hard

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

DSA Javascript

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

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

Avalue

Bchildren

Cchild

Dval

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing to val which is undefined.

Looping over child which is a variable, not a property.

Looping over node which is an object, not iterable.

Compare node.value to the value parameter and loop over children array.

5fill in blank

hard

Fill all three blanks to create a function that collects all values in a tree into an array.

DSA Javascript

function collectValues(node) {
  let values = [[1]];
  for (const child of node.[2]) {
    values = values.concat(collectValues([3]));
  }
  return values;
}

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

Anode.value

Bchildren

Cchild

Dnode

Attempts:

3 left

💡 Hint

Common Mistakes

Using node instead of child in recursion.

Using node.children inside the loop instead of child.

Starting values with an empty array instead of including current node's value.

Start with the current node's value, loop over children, and recursively collect values from each child.