In Jeff Erickson's Algorithms textbook, the chapter on Dynamic Programming asks you to "Describe an efficient algorithm to compute the length of the shortest oscillating supersequence of an arbitrary array A of integers".
A supersequence contains all of the elements from the original array X[1...n], and oscillating is defined as X [i] < X [i + 1] for all even i, and X [i] > X [i + 1] for all odd i.
However, I am not asking about the answer to this problem. I am just wondering if this question even is sound. How can you find a supersequence of a single array? Wouldn't the answer just be the length of the original array if all elements are oscillating? Else, 0. Usually, a supersequence is found between multiple arrays.