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APL is the language I only ever see around AoC. But it's so impressive too. Like the first part of today's solution is "+/¯1↓x<1⊖x" (stolen from someone on Redd

APL is the language I only ever see around AoC. But it's so impressive too. Like the first part of today's solution is "+/¯1↓x<1⊖x" (stolen from someone on Reddit) and I'm like.. ok, I need to learn this language one day. (Since their solution is now being discussed, it's from here: https://www.reddit.com/r/adventofcode/comments/r66vow/2021_day_1_solutions/hmsacv9/ https://www.reddit.com/r/adventofcode/comments/r66vow/2021_d...)

maximus-decimus 5y ago
and this is the solution in Q, including paring the file: `(+/) 1_ (>':) "I" $ read0 `:input_1.txt` I don't think their second solution actually works unless I'm missing something though : +/¯3↓x<3⊖x This compares every element to the the one 3 positions before it, when the question was to take the sum of each 3 elements and check if it's smaller than the previous sum.
ollran 5y ago
APL is quite common in the code golf scene.
Jtsummers 5y ago
Interesting solution. 1⊖x Rotates the sequence so the first becomes the last. x < 1⊖x Element-wise compare each, resulting in a list of 1s and 0s ¯1 ↓ x<1⊖x Drop the last element because it's actually not part of the solution (thanks to the earlier rotation). +/ ¯1↓x<1⊖x Sum all of them, since it's just 1s and 0s this gives a correct count. Part 2 is solvable (unless I missed something, works on the sample data) by just changing two characters from that solution. Neat.
- petercooper 5y ago
  Thanks for the explanation! I just found someone with a different approach who has similarly broken it down on Twitter: https://twitter.com/janiczek/status/1465969017089363969 https://twitter.com/janiczek/status/1465969017089363969
  - Jtsummers 5y ago
    https://tryapl.org https://tryapl.org That's an online APL REPL with all the symbols listed at the top, hover to get a tooltip that tells you both how to type it into the REPL and what its name is. I'd forgotten what rotate was because my APL deep-dive was 2 or 3 years ago now. It's handy for discovering the symbols and breaking down the harder-to-understand one-liners (for novices or those unfamiliar with it).

maximus-decimus 5y ago

and this is the solution in Q, including paring the file: `(+/) 1_ (>':) "I" $ read0 `:input_1.txt` I don't think their second solution actually works unless I'm missing something though : +/¯3↓x<3⊖x This compares every element to the the one 3 positions before it, when the question was to take the sum of each 3 elements and check if it's smaller than the previous sum.

ollran 5y ago

APL is quite common in the code golf scene.

Jtsummers 5y ago

Interesting solution. 1⊖x Rotates the sequence so the first becomes the last. x < 1⊖x Element-wise compare each, resulting in a list of 1s and 0s ¯1 ↓ x<1⊖x Drop the last element because it's actually not part of the solution (thanks to the earlier rotation). +/ ¯1↓x<1⊖x Sum all of them, since it's just 1s and 0s this gives a correct count. Part 2 is solvable (unless I missed something, works on the sample data) by just changing two characters from that solution. Neat.

petercooper 5y ago
Thanks for the explanation! I just found someone with a different approach who has similarly broken it down on Twitter: https://twitter.com/janiczek/status/1465969017089363969 https://twitter.com/janiczek/status/1465969017089363969
- Jtsummers 5y ago
  https://tryapl.org https://tryapl.org That's an online APL REPL with all the symbols listed at the top, hover to get a tooltip that tells you both how to type it into the REPL and what its name is. I'd forgotten what rotate was because my APL deep-dive was 2 or 3 years ago now. It's handy for discovering the symbols and breaking down the harder-to-understand one-liners (for novices or those unfamiliar with it).