Heap Extract Min or Max Bubble Down in DSA Javascript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get the left child index in a heap array.

DSA Javascript

function leftChildIndex(parentIndex) {
  return 2 * parentIndex [1] 1;
}

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A+

B-

C/

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction instead of addition

Using division or multiplication incorrectly

The left child index in a heap is calculated as 2 * parentIndex + 1.

2fill in blank

medium

Complete the code to swap two elements in the heap array.

DSA Javascript

function swap(heap, i, j) {
  const temp = heap[i];
  heap[i] = heap[[1]];
  heap[j] = temp;
}

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Aheap

Bi

Cj

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping with wrong indices

Using variable names incorrectly

To swap elements at indices i and j, assign heap[i] = heap[j].

3fill in blank

hard

Fix the error in the bubbleDown function to correctly compare and swap with the smaller child in a min-heap.

DSA Javascript

function bubbleDown(heap, index) {
  const left = 2 * index + 1;
  const right = 2 * index + 2;
  let smallest = index;

  if (left < heap.length && heap[left] [1] heap[smallest]) {
    smallest = left;
  }
  if (right < heap.length && heap[right] < heap[smallest]) {
    smallest = right;
  }
  if (smallest !== index) {
    swap(heap, index, smallest);
    bubbleDown(heap, smallest);
  }
}

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A<

B>

C==

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using greater than instead of less than

Using equality instead of comparison

In a min-heap, we swap if the child is smaller than the current smallest, so the comparison is <.

4fill in blank

hard

Fill both blanks to complete the extractMin function that removes the smallest element and restores the heap.

DSA Javascript

function extractMin(heap) {
  if (heap.length === 0) return null;
  const min = heap[0];
  heap[0] = heap[[1]];
  heap.[2]();
  bubbleDown(heap, 0);
  return min;
}

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Aheap.length - 1

Bpop()

Cshift()

Dlength

Attempts:

3 left

💡 Hint

Common Mistakes

Using shift() which removes first element

Not removing last element after replacement

Replace root with last element (heap.length - 1) and remove last element with pop().

5fill in blank

hard

Fill all three blanks to complete the bubbleDown function for a max-heap that swaps with the larger child.

DSA Javascript

function bubbleDown(heap, index) {
  const left = 2 * index + 1;
  const right = 2 * index + 2;
  let largest = index;

  if (left < heap.length && heap[left] [1] heap[largest]) {
    largest = left;
  }
  if (right < heap.length && heap[right] [2] heap[largest]) {
    largest = right;
  }
  if (largest !== index) {
    swap(heap, index, largest);
    bubbleDown(heap, [3]);
  }
}

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A>

B<

Clargest

Dindex

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong comparison operators

Recursing on wrong index

For max-heap, swap if child is greater (use > for comparison), and recurse on largest child index.