Pair Sum in a Sorted List

You're given an array nums and a number target. nums is sorted in non-decreasing order: each number is greater than or equal to the one before it. Find two different positions i < j where nums[i] + nums[j] === target.

• Return the 0-based indices as [i, j].
• At most one pair of positions works. If no pair works, return [].
• nums can contain negative numbers and duplicates. It can have up to 100,000 elements.
• Use O(1) extra memory, which means a fixed amount that doesn't grow with nums. So don't use a map or a set.