See: https://adventofcode.com/2015/day/1
** Part 1
*** Purpose
Given a stream of parenthesis:

#+begin_example
))(((((
#+end_example

We subtract the number of "((" parens from the number of ")))".

*** Method
The solution to this is simple: count the number of each, and perform the subtraction. Given that I already solved part on of this problem before, I will instead immediately design a solution to the problem that also works for part 2. In my attempt months ago, I made the "mistake" of not using a loop :):

** Part 2
*** Purpose
Now, we need to calculate the index of the input stream where the cumulative number is first zero.

*** Method
The above information reveals that a solution that would work for both parts is a simple loop structure.