Write a function named is_sorted accepts an array stack of numbers as a parameter
and returns true if the elements in the stack occur in ascending
(non-decreasing) order from top to bottom, else false. That is, the smallest
element should be on top, growing larger toward the bottom. An empty or one-element stack is
considered to be sorted.
For example, if passed the following stack, your function should return true:
bottom [20, 20, 17, 11, 8, 8, 3, 2] top
The following stack is not sorted (the 15 is out of place), so passing it to your function
should return false:
bottom [18, 12, 15, 6, 1] top
When your function returns, the stack should be in the same state as when it was passed in.
In other words, if your function modifies the stack, you must restore it before returning.
Constraints:
- You may use one array as your only temorary data structure.
- Your solution should run in O(N) time, where N is the number of elements of the stack.
