Solved Problem 13 but

I'm not happy about it. I was on the road to an intelligent solution, but it
occurred to me that I can actually add all the numbers as they are, so that's
what I did. There's a lot of code I can clean up here.
Problem 14 solved

I just brute-forced it. It took <= 15 minutes, because I started it, walked to
class, and it was done when I got there. I imagine there are a lot of things I
can improve in this code--i.e. not calling (length ls)...