Top K Frequent Elements

Problem

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

Example

nums = [1,1,1,2,2,3], k = 2
Output: [1, 2]

Constraints

• 1 ≤ nums.length ≤ 10^5
• k is in the range [1, number of unique elements]
• The answer is guaranteed to be unique

Expected complexity

Better than O(n log n). Can you solve it in O(n) using bucket sort?