LeetCode 347 Top K Frequent Elements - Problem Statement

Given an integer array nums and an integer k, return the k most frequent elements. You can return the answer in any order.

For example, nums = [1, 1, 1, 2, 2, 3] with k = 2 returns [1, 2]. Element 1 appears $3$ times, 2 appears twice. Those are the top $2$ by frequency.

Think about how you'd count frequencies first. Then ask: how do you efficiently find the top k without sorting all elements?

Constraints: $1 \le n \le 10^5$, $k$ is always valid (at most the number of unique elements).