Read the stack size
Updated
Size is a count you can read in O(1) if you store it, or O(n) if you walk a list-backed stack without a counter. Prefer a stored size.
What to focus on
size() does not change the stack. size 0 iff isEmpty. After push, size+1; after pop, size−1. Do not confuse size with the top value.
Worked examples
three
a = [4, 1, 9]- count 3
Result: 3
after push
a = [4, 1, 9], push 8- 4
Result: 4
empty
a = []- 0
Result: 0
Try it
Write size(a). a is the stack, written [bottom, ..., top]. Return the count. Do not change the stack. Size is not the top value. Print 3 for [4, 1, 9], 4 after push 8, 0 for [].
Values are integers. The stack may be empty.