Build Heap from Array Heapify in DSA Javascript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get the index of the left child 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 multiplication or division incorrectly.

In a heap stored as an array, the left child of a node at index i is at 2*i + 1.

2fill in blank

medium

Complete the code to swap two elements in the array.

DSA Javascript

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

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Aarr

Bi

Cj

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using the same index for both assignments.

Using an invalid variable.

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

3fill in blank

hard

Fix the error in the heapify function to correctly compare and swap with the largest child.

DSA Javascript

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

  if (left < n && arr[left] [1] arr[largest]) {
    largest = left;
  }

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

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

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A>

B<

C==

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' in comparison.

Using equality or inequality operators incorrectly.

To build a max heap, we check if the left child is greater than the current largest. The condition should be arr[left] > arr[largest]. The error was using '<' which is incorrect.

4fill in blank

hard

Fill both blanks to complete the buildHeap function that heapifies from the last parent to the root.

DSA Javascript

function buildHeap(arr) {
  const n = arr.length;
  for (let i = [1]; i >= 0; i--) {
    heapify(arr, n, [2]);
  }
}

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AMath.floor(n / 2) - 1

B0

Cn - 1

Di

Attempts:

3 left

💡 Hint

Common Mistakes

Starting from 0 instead of last parent.

Using wrong index in heapify call.

Heapify starts from the last parent node at index Math.floor(n/2) - 1 down to 0. The loop variable i is used in heapify call.

5fill in blank

hard

Fill all three blanks to complete the heapify function that maintains max heap property.

DSA Javascript

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

  if (left < n && arr[left] [1] arr[largest]) {
    largest = left;
  }

  if (right < n && arr[right] [2] arr[largest]) {
    largest = right;
  }

  if (largest !== i) {
    [3](arr, i, largest);
    heapify(arr, n, largest);
  }
}

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

A>

B<

Cswap

Dheapify

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' in comparisons.

Calling heapify instead of swap to exchange elements.

To maintain max heap, compare children with '>' operator and swap if needed using swap function.