In section a:
I saw there was some discussion of this in previous posts, but just to be clear - can I assume that the array starts out filled with n elements, n being the number operations I will then perform? I can get an n^2 expression this way, but only if I mix up the meanings of the "number of elements" n and the "number of operations" n. Is this O.K?
In section b:
1. Can I assume that "starting with an empty stack" means the first member I enter sits in an array of size 1?
2. There appears to be a discrepancy between stating that the array is halved once it holds less members than one quarter of its size and stating that the new array will be half full. Suppose I added members, and now have an array of size 8. Now I start removing them. I will only have less than one quarter when I hold 1 member in the array. At which point, the new array of size 4 will also hold one member, which is less than half. How do you resolve this? And if it doesn't really matter all that much, please say so too…
3. Do I need to solve this question by showing the w.c. series of n actions will cost no more than O(n)? Is an intuitive explanation of what series of actions makes up the w.c. satisfactory?