Moderate Heap Question 115 of 224

How do you find the k most frequent elements in an array?

DSA interview set · Speak this in 60–90 seconds · Faridabad & Delhi NCR

PICTURE THIS: ARRAY IN MEMORY

01234

Index starts at 0. Scan once for max — O(n).

Simple meaning

Count frequencies in a hash map, then push (freq, value) into a min-heap of size k.

WHY — Heap instead of guessing?

Why interviewers care about Heap:

This is a process

question about Heap.

Panels listen for order,

trade-offs, and what you would actually do on a DSA project - not buzzwords.

Stay structured

Name the idea, why it exists, then one short example.

Close cleanly

End with when you use it and one common pitfall.

STEPS — What happens step by step?

Before you speak the answer, walk the interviewer through these steps:

1
Count frequencies in a
hash map, then push (freq, value) into a min-heap of size k.
2
Counting is O(n) and
the heap is O(u log k) for u unique keys, space O(u).
3
A max-heap of all
uniques is O(u log u)
4
bucket sort by frequency
can be O(n).
5
Common mistake
What juniors usually get wrong.
6
Close
When you pick this over the alternative.

EXAMPLE — See it in action

Here's a short line you can speak, broken into clear beats:

Say this line

“Counting is O(n) and the heap is O(u log k) for u unique keys, space O(u).”

Break into beats

CountingisOnandthe

Speaking order

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Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.

Key takeaway

Count frequencies in a hash map, then push (freq, value) into a min-heap of size k. Counting is O(n) and the heap is O(u log k) for u unique keys, space O(u).