Efficiently get sorted sums of a sorted list

Question

You have an ascending list of numbers, what is the most efficient algorithm you can think of to get the ascending list of sums of every two numbers in that list. Duplicates in

Answer 1

No matter what you do, without additional constraints on the input values, you cannot do better than O(n^2), simply because you have to iterate through all pairs of numbers. The iteration will dominate sorting (which you can do in O(n log n) or faster).