Top K Frequent Elements Using Heap in DSA Javascript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a frequency map of elements in the array.

DSA Javascript

const freqMap = new Map();
for (const num of nums) {
  freqMap.set(num, (freqMap.get(num) || 0) [1] 1);
}

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

A+

B-

C/

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction or multiplication instead of addition.

We add 1 to the current count or start from 0 if the element is not yet in the map.

2fill in blank

medium

Complete the code to push elements into the heap with their frequency.

DSA Javascript

for (const [num, freq] of freqMap.entries()) {
  heap.push({ val: num, freq: freq });
  heap.sort((a, b) => b.freq [1] a.freq);
}

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

A*

B+

C/

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using addition or multiplication in the sort comparator.

We sort the heap so the element with the highest frequency comes first by subtracting frequencies.

3fill in blank

hard

Fix the error in the code that extracts the top k frequent elements from the heap.

DSA Javascript

const result = [];
for (let i = 0; i < k; i++) {
  result.push(heap.[1]().val);
}

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Ashift

Bpop

Cpush

Dunshift

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop() which removes the last element instead of the first.

Since the heap is sorted descending, we remove the first element with shift() to get the top frequency.

4fill in blank

hard

Fill both blanks to complete the function that returns the top k frequent elements.

DSA Javascript

function topKFrequent(nums, k) {
  const freqMap = new Map();
  for (const num of nums) {
    freqMap.set(num, (freqMap.get(num) || 0) [1] 1);
  }
  const heap = [];
  for (const [num, freq] of freqMap.entries()) {
    heap.push({ val: num, freq: freq });
    heap.sort((a, b) => b.freq [2] a.freq);
  }
  const result = [];
  for (let i = 0; i < k; i++) {
    result.push(heap.shift().val);
  }
  return result;
}

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

A+

B-

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up operators for counting and sorting.

The frequency map increments counts with +1, and the heap sorts descending by subtracting frequencies.

5fill in blank

hard

Fill all three blanks to complete the function using a heap to find top k frequent elements.

DSA Javascript

function topKFrequent(nums, k) {
  const freqMap = new Map();
  for (const num of nums) {
    freqMap.set(num, (freqMap.get(num) || 0) [1] 1);
  }
  const heap = [];
  for (const [num, freq] of freqMap.entries()) {
    heap.push({ val: num, freq: freq });
    heap.sort((a, b) => b.freq [2] a.freq);
  }
  const result = [];
  for (let i = 0; i < k; i++) {
    result.push(heap.[3]().val);
  }
  return result;
}

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

A+

B-

Cshift

Dpop

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop() instead of shift() to remove elements.

Increment frequency with +, sort descending with -, and remove first element with shift().