Given an unsorted integer array `nums` of length `N` and an integer `k` such that `1 <= k <= N`, return the `k` largest elements in the array. If a value appears multiple times, treat each occurrence separately. You may return the result in any order. Assume `N` is much larger than `k`, so the goal is to design a solution that is more efficient than sorting the entire array when possible. Example: - Input: `nums = [7, 10, 4, 3, 20, 15]`, `k = 3` - Output: `[10, 15, 20]` Follow-up: If you choose a heap-based solution, explain whether a min-heap or a max-heap is the better choice and why.