I wrote a working algorithm to recursively find every version of XMAS IF you were allowed to change directions each time. So I misread the prompt. I thought this was valid:
X - - -
- M - -
- - A -
- S - -
This meant checking every direction for a valid next letter, every single time. Which (a) was a natural fit for recursion, and (b) generated way too many matches, and (c) literally isn't the problem, lol.
Takeaways today:
- Read your problem thoroughly. Read examples.
- If you're ever nesting loops very deeply, or reaching for loop labels, make a function instead.
- It's okay to be a bit redundant for the sake of simplicity. I over-check both part 1 and part 2, but being more efficient (fewer loops) would require managing more state for part 2. For part 1, it'd just be an early-exit, which isn't at all a big deal and is totally a low-hanging fruit win.
- Part 2 allows you to only examine
(rows - 1) x (cols - 1)for dimension - an X-MAS can't start on a corner or edge. Nice! - Extracting out the corners for part 2 in order and then comparing to valid slice orders (e.g.
[M M S S]) makes it much easier, plus you can rotate one valid arrangement around to get your permutations of valid orderings.