Maximize min+max of contiguous subarray

You are given an array of **n** positive integers `nums`. Find a **contiguous subarray** that contains **at least two elements** and maximizes the value: > (minimum element of the subarray) + (maximum element of the subarray) Return this maximum possible sum. If multiple subarrays yield the same maximum sum, you only need to return the value of that sum (not the subarray itself). You may assume `n ≥ 2`. --- **Example** Input: ```text nums = [5, 12, 9, 6, 4] ``` All valid subarrays of length ≥ 2 and their `(min + max)` values include: - `[5, 12]` → min = 5, max = 12, sum = 17 - `[5, 12, 9]` → min = 5, max = 12, sum = 17 - `[12, 9]` → min = 9, max = 12, sum = 21 - `[12, 9, 6]` → min = 6, max = 12, sum = 18 - `[9, 6]` → min = 6, max = 9, sum = 15 - ... The maximum possible value of `min + max` is `21`, from subarray `[12, 9]`. **Output:** ```text 21 ```