Find all differences in an array in O(n)

Question

Question: Given a sorted array A find all possible difference of elements from A.

My solution:

for (int i=0; i

        

Answer 1

For example for an array with the elements {2¹, 2², ..., 2ⁿ} there are n⋅(n-1)/2 possible differences, and no two of them are equal. So there are O(n²) differences.

Since you have to enumerate all of them, you also need at least O(n²) time.