Min Heap vs Max Heap When to Use Which in DSA Javascript - Interactive Comparison Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a min heap by using the correct comparison operator.

DSA Javascript

function compare(a, b) { return a [1] b; } // For min heap

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

A>

B<

C===

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' instead of '<' will create a max heap instead.

For a min heap, the comparison should return true when a is less than b, so the smallest element rises to the top.

2fill in blank

medium

Complete the code to create a max heap by using the correct comparison operator.

DSA Javascript

function compare(a, b) { return a [1] b; } // For max heap

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

A<

B===

C>

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' will create a min heap instead.

For a max heap, the comparison should return true when a is greater than b, so the largest element rises to the top.

3fill in blank

hard

Fix the error in the code that builds a min heap by choosing the correct comparison operator.

DSA Javascript

function buildHeap(arr) { return arr.sort((a, b) => a [1] b ? -1 : 1); } // Min heap

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

A>

B!=

C===

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' sorts descending, which is for max heap.

Sorting with a < b ensures the smallest elements come first, which is needed for a min heap.

4fill in blank

hard

Fill both blanks to complete the function that decides which heap to use based on the need for smallest or largest element retrieval.

DSA Javascript

function chooseHeap(type) {
  if (type === 'min') return [1];
  else if (type === 'max') return [2];
  else return null;
}

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

AMinHeap

BMaxHeap

CHeap

DPriorityQueue

Attempts:

3 left

💡 Hint

Common Mistakes

Returning generic Heap or PriorityQueue instead of specific heap types.

Return MinHeap when the smallest element is needed, and MaxHeap when the largest element is needed.

5fill in blank

hard

Fill all three blanks to complete the code that inserts a new element into a heap and maintains the heap property.

DSA Javascript

function insert(heap, element) {
  heap.push(element);
  let index = heap.length - 1;
  while (index > 0) {
    let parent = Math.floor((index - 1) / 2);
    if (heap[parent] [1] heap[index]) break;
    [heap[parent], heap[index]] = [heap[index], heap[parent]];
    index = parent;
  }
  return heap;
}

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

A<

B>

C<=

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' instead of '<' breaks max heap property.

For a max heap insertion, swap if parent is less than child (parent < child), so the largest element stays on top.

Practice

1. Which heap type is best suited when you need to quickly find the smallest element in a collection?

easy

A. Binary Search Tree

B. Min Heap

C. Max Heap

D. Hash Table

Solution

1. Step 1: Understand the heap types

   A Min Heap always keeps the smallest element at the root, making it easy to access.

2. Step 2: Match the requirement with heap property

   Since we want quick access to the smallest element, Min Heap is the best choice.

3. Final Answer:

   Min Heap -> Option B

4. Quick Check:

   Smallest element = Min Heap [OK]

Hint: Smallest element? Use Min Heap [OK]

Common Mistakes:

• Confusing Min Heap with Max Heap
• Choosing data structures unrelated to heaps
• Thinking Max Heap gives smallest element

2. Which of the following is the correct way to insert an element into a Max Heap in JavaScript?

easy

A. Add element at the end and heapify down

B. Add element at root and heapify down

C. Add element at the end and heapify up

D. Add element at root and heapify up

Solution

1. Step 1: Recall Max Heap insertion process

   New elements are added at the end (bottom level) to maintain complete tree property.

2. Step 2: Restore heap property by heapifying up

   After insertion, heapify up swaps the new element with parents if larger, to maintain Max Heap.

3. Final Answer:

   Add element at the end and heapify up -> Option C

4. Quick Check:

   Insert = end + heapify up [OK]

Hint: Insert at end, then heapify up for Max Heap [OK]

Common Mistakes:

• Heapifying down after insertion
• Inserting at root directly
• Confusing heapify direction

3. Consider the following JavaScript code using a Min Heap implementation:

const minHeap = new MinHeap();
minHeap.insert(10);
minHeap.insert(5);
minHeap.insert(20);
minHeap.insert(3);
console.log(minHeap.extract());

What will be printed?

medium

A. 20

B. 10

C. 5

D. 3

Solution

1. Step 1: Insert elements into Min Heap

   Elements 10, 5, 20, 3 are inserted. Min Heap keeps smallest element at root.

2. Step 2: Extract removes and returns the smallest element

   Extract returns the root, which is the smallest: 3.

3. Final Answer:

   3 -> Option D

4. Quick Check:

   Min Heap extract = smallest element [OK]

Hint: Extract from Min Heap returns smallest [OK]

Common Mistakes:

• Thinking extract returns largest
• Confusing Min Heap with Max Heap
• Ignoring heap property after insertions

4. You have a Max Heap implementation but notice that after inserting a new element, the heap property is violated. Which of the following is the most likely cause?

medium

A. Heapify down was called instead of heapify up after insertion

B. Element was inserted at the root instead of the end

C. Heapify up was called twice

D. Heapify down was not called after extraction

Solution

1. Step 1: Understand insertion in Max Heap

   Insertion adds element at the end and restores heap by heapifying up.

2. Step 2: Identify error from heapify direction

   Calling heapify down after insertion won't fix the heap property properly, causing violation.

3. Final Answer:

   Heapify down was called instead of heapify up after insertion -> Option A

4. Quick Check:

   Insert needs heapify up, not down [OK]

Hint: Insertion needs heapify up, not down [OK]

Common Mistakes:

• Inserting at root directly
• Confusing heapify directions
• Ignoring heapify after insertion

5. You need to design a system that always returns the median of a stream of numbers efficiently. Which combination of heaps is best to use and why?

hard

A. One Max Heap for lower half and one Min Heap for upper half

B. Two Max Heaps to store all numbers

C. One Min Heap for lower half and one Max Heap for upper half

D. Two Min Heaps to store all numbers

Solution

1. Step 1: Understand median calculation from stream

   Median splits data into lower half and upper half; median is middle value(s).

2. Step 2: Use Max Heap for lower half and Min Heap for upper half

   Max Heap keeps largest of lower half, Min Heap keeps smallest of upper half, enabling quick median calculation.

3. Final Answer:

   One Max Heap for lower half and one Min Heap for upper half -> Option A

4. Quick Check:

   Median = Max Heap (low) + Min Heap (high) [OK]

Hint: Median needs Max Heap low + Min Heap high [OK]

Common Mistakes:

• Using two heaps of same type
• Mixing heap roles incorrectly
• Not balancing heaps sizes