Quickselect: Find the K-th element (with large-scale follow-up)

Problem Given an integer array nums of length n (may contain duplicates) and an integer k, return the k-th largest element in the array (k-th by value order, not the k-th distinct element). Requirements Implement an average O(n) solution (e.g., using Quickselect). Follow-up (very large data): when n is extremely large (cannot fit into memory at once) or you need more stable performance, describe/implement an alternative (e.g., using a heap). I/O Format Input: Line 1: integer n Line 2: n integers (the array) Line 3: integer k Output: One line: the k-th largest element Constraints 1 <= n <= 2 * 10^5 -10^9 <= nums[i] <= 10^9 1 <= k <= n Example Input: 6 3 2 1 5 6 4 2 Output: 5 Example Input 6 3 2 1 5 6 4 2 Output 5