Day 2: Red-Nosed Reports
Megathread guidelines
- Keep top level comments as only solutions, if you want to say something other than a solution put it in a new post. (replies to comments can be whatever)
- You can send code in code blocks by using three backticks, the code, and then three backticks or use something such as https://blocks.programming.dev if you prefer sending it through a URL
FAQ
- What is this?: Here is a post with a large amount of details: https://programming.dev/post/22323136
- Where do I participate?: https://adventofcode.com/
- Is there a leaderboard for the community?: We have a programming.dev leaderboard with the info on how to join in this post: https://programming.dev/post/6631465
Uiua
Uiua is still developing very quickly, and this code uses the experimental tuples function, hence the initial directive.
# Experimental!
"7 6 4 2 1\n1 2 7 8 9\n9 7 6 2 1\n1 3 2 4 5\n8 6 4 4 1\n1 3 6 7 9"
⊜(⊜⋕⊸≠@\s)⊸≠@\n # Partition at \n, then at space, parse ints.
IsSorted ← +⊃(≍⇌⍆.|≍⍆.) # Compare with sorted array.
IsSmall ← /××⊃(>0|<4)⌵↘¯1-↻1. # Copy offset by 1, check diffs.
IsSafe ← ×⊃IsSmall IsSorted # Safe if Small steps and Ordered.
IsSafer ← ±/+≡IsSafe ⧅<-1⧻. # Choose 4 from 5, check again.
&p/+≡IsSafe . # Part1 : Is each row safe?
&p/+≡(±+⊃IsSafe IsSafer) # Part2 : Is it safe or safer?
This looks so alien! Does it work with the full set? The comment says 5, choose 4, but I guess it’s written as n, choose n-1?
Yes, it should do. I do run the solutions against the live data, but sometimes tweak the solutions afterwards, so can’t always guarantee them :-). I left the comment as 5 choose 4 as it felt clearer in the context of the test data.
It does still feel very alien at times, but I do love being able to think about how to adopt a more arrays-based approach to solving these problems.
How do you write this, not conceptually but physically. Do you have a char picker open at all times?
Haha, you can do it that way, in fact the online Uiua Pad editor has all the operators listed along the top.
But all the operators have ascii names, so you can type e.g.
IsSmall = reduce mul mul fork(>0|<4) abs drop neg 1 - rot 1 dup
and the formatter will reduce that to
IsSmall ← /××⊃(>0|<4)⌵↘¯1-↻1.
whenever you save or execute code.
That works in the Pad, and you can enable similar functionality in other editors.