Heap Sort Algorithm in DSA Javascript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to swap two elements in the array.

DSA Javascript

function swap(arr, i, j) {
  let temp = arr[i];
  arr[i] = arr[1]j;
  arr[j] = temp;
}

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

A+

B-

C[

D.

Attempts:

3 left

💡 Hint

Common Mistakes

Using dot notation instead of square brackets to access array elements.

Using plus or minus signs which are arithmetic operators, not for indexing.

We use square brackets to access array elements by index in JavaScript.

2fill in blank

medium

Complete the code to heapify a subtree rooted at index i.

DSA Javascript

function heapify(arr, n, i) {
  let largest = i;
  let left = 2 * i + 1;
  let right = 2 * i + [1];

  if (left < n && arr[left] > arr[largest]) {
    largest = left;
  }

  if (right < n && arr[right] > arr[largest]) {
    largest = right;
  }

  if (largest !== i) {
    swap(arr, i, largest);
    heapify(arr, n, largest);
  }
}

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

A0

B3

C1

D2

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1 instead of 2 for the right child index.

Using 3 or 0 which are incorrect for child indexing.

The right child index in a heap is calculated as 2 * i + 2, so the blank should be 2.

3fill in blank

hard

Fix the error in the loop that builds the max heap.

DSA Javascript

for (let i = Math.floor(n / 2) - 1; i [1] 0; i--) {
  heapify(arr, n, i);
}

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

A>=

B<=

C<

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' or '<=' which causes the loop to skip the root node.

Using '>' which causes an infinite loop.

The loop should run while i is greater than or equal to 0 to cover all parent nodes.

4fill in blank

hard

Fill both blanks to complete the heap sort main loop.

DSA Javascript

for (let i = n - 1; i > [1]; i--) {
  swap(arr, 0, i);
  heapify(arr, i, [2]);
}

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

A0

B1

Ci

Dn

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1 or n instead of 0 for heapify starting index.

Using i instead of 0 for heapify starting index.

We swap the root (index 0) with the last element and then heapify from the root (index 0).

5fill in blank

hard

Fill all three blanks to complete the heap sort function.

DSA Javascript

function heapSort(arr) {
  let n = arr.length;

  for (let i = Math.floor(n / 2) - 1; i [1] 0; i--) {
    heapify(arr, n, i);
  }

  for (let i = n - 1; i > [2]; i--) {
    swap(arr, 0, i);
    heapify(arr, i, [3]);
  }
}

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

A>=

B>

C0

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' or '<=' in the first loop condition.

Using 1 instead of 0 for heapify starting index.

Using '>=' instead of '>' in the second loop condition.

The first loop runs while i >= 0, the second while i > 0, and heapify starts at index 0.