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

Practice - 5 Tasks

1fill in blank

easy

Complete the code to count the frequency of each number in the array.

DSA Typescript

const frequencyMap = new Map<number, number>();
for (const num of nums) {
  frequencyMap.set(num, (frequencyMap.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 '-' instead of '+' will decrease the count.

Using '*' or '/' will not correctly count frequency.

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

2fill in blank

medium

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

DSA Typescript

for (const [num, freq] of frequencyMap.entries()) {
  heap.push({ value: num, priority: [1] });
}

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

Afreq

Bnum

Cfreq + 1

Dfreq - 1

Attempts:

3 left

💡 Hint

Common Mistakes

Multiplying or dividing frequency changes the priority incorrectly.

Subtracting 1 may cause wrong priority.

We use the frequency directly as the priority for the heap element.

3fill in blank

hard

Fix the error in the code to maintain the heap size at most k by removing the smallest frequency element.

DSA Typescript

if (heap.size() > k) {
  heap.[1]();
}

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Ainsert

Bpush

Cpeek

Dpop

Attempts:

3 left

💡 Hint

Common Mistakes

Using push or insert adds elements instead of removing.

peek only returns the top without removing.

We remove the smallest element using pop to keep the heap size at most k.

4fill in blank

hard

Fill both blanks to extract the top k frequent elements from the heap into the result array.

DSA Typescript

const result: number[] = [];
while (heap.size() > 0) {
  const top = heap.[1]();
  result.[2](top.value);
}

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Apop

Bpush

Cpeek

Dshift

Attempts:

3 left

💡 Hint

Common Mistakes

Using peek does not remove elements from the heap.

Using shift is for arrays, not heaps.

We remove the smallest element with pop and add its value to the result with push.

5fill in blank

hard

Fill all three blanks to return the result array reversed so the most frequent elements come first.

DSA Typescript

return result.[1]().[2]((a, b) => b [3] a);

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Areverse

Bsort

C-

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' in the sort comparison will not sort correctly.

Not reversing will give least frequent first.

We reverse the array and then sort it in descending order by frequency using subtraction.