I came across my 10 year old repo for project Euler solutions. (N.B! Euler spoilers onwards).

Naturally it’s full of python files. One file stood out. It was just called problem15.txt.

I pulled up the problem.

I imagined getting this at work. I think I would reach for python. Maybe start with a naive brute force. Throw a bunch of loops together. If that didn’t solve it, reach for memoization. Dynamic programming, let’s go! (this is just me fantasizing. At work I would just give it to an AI and continue with my day)

And let’s see how I solved it when I was still an engineering student

problem15.txt⌗

doesnt even need to program anything for this problem
there are 6 solutions to the 2x2 grid
there are 2 solutions to 1x1 grid
there are 20 solutions to a 3x3 grid
this follows the pattern of (2n) choose n
so (2*20) choose 20 = 137846528820

(If you aren’t familiar with discrete math, see the binomial coefficient for syntax)

I’m impressed by past self! And present me became sad. It feels like an Asimov book where the main character finds past knowledge, codified by the ancients. But it’s just me when I was in school.

I remixed this picture to cope.