Top K Frequent Words

Question

## Problem

Given a list of words, return the k most frequent, sorted by frequency then lexicographically.

## Example
```
["i","love","leetcode","i","love","coding"], k=2 -> ["i","love"]
```

## Constraints
- 1 ≤ words.length ≤ 10^4

## Approach
Count map + heap with custom comparator. Reported Box question.