AoC 2025 - Day 1

Author: dunhamsteve

aoc2025/Aoc.newt

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+module Aoc
+
+import Prelude
+
+-- `by` is the first argument for use in `map`
+nums' : String → String → List Int
+nums' by s = map stringToInt $ filter (_/=_ "") $ split (trim s) by
+
+nums : String → List Int
+nums s = map stringToInt $ filter (_/=_ "") $ split (trim s) " "
+
+indexOf? : ∀ a. {{Eq a}} → a → List a → Maybe Nat
+indexOf? {a} z xs = go Z z xs
+  where
+    go : Nat → a → List a → Maybe Nat
+    go ix z Nil = Nothing
+    go ix z (x :: xs) =
+      if z == x then Just ix else go (S ix) z xs
+
+-- TODO move to Aoc library
+Point : U
+Point = Int × Int
+
+instance Add Point where
+  (a,b) + (c,d) = (a + c, b + d)
+
+instance Sub Point where
+  (a,b) - (c,d) = (a - c, b - d)
+
+
+
+-- instance Ord Point where
+--   (a,b) < (c,d) = a < c || a == c && b < d
+
+-- instance Eq Point where
+--   (a,b) == (c,d) = a == c && b == d

aoc2025/Data

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+../src/Data

aoc2025/Day1.newt

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+module Day1
+
+import Prelude
+import Node
+
+parseLine : String → Maybe Int
+parseLine s = case unpack s of
+  ('L' :: rest) => Just $ 0 - stringToInt (pack rest)
+  ('R' :: rest) => Just $ stringToInt (pack rest)
+  _ => Nothing
+
+parse : String → List Int
+parse text = mapMaybe parseLine $ split (trim text) "\n"
+
+part1 : List Int → Int
+part1 xs = go 0 50 xs
+  where
+    go : Int → Int → List Int → Int
+    go acc pos Nil = acc
+    go acc pos (x :: xs) =
+      let pos = mod (x + pos)  100
+          acc = if pos == 0 then acc + 1 else acc
+      in go acc pos xs
+
+-- This is uglier than I'd like
+part2 : List Int → Nat
+part2 xs = go Z 50 xs
+  where
+    go : Nat → Int → List Int → Nat
+    go acc pos Nil = acc
+    go acc pos (0 :: xs) = go acc pos xs
+    go acc pos (x :: xs) =
+      if x == 0 then go acc pos xs
+      else if x <= -100 then go (S acc) pos (x + 100 :: xs)
+      else if 100 <= x then go (S acc) pos (x - 100 :: xs)
+      else if x + pos < 0 then go (if pos == 0 then acc else S acc) (x + pos + 100) xs
+      else if x + pos == 0 then go (S acc) (x + pos) xs
+      else if 100 <= x + pos  then go (S acc) (x + pos - 100) xs
+      else go acc (x + pos) xs
+
+run : String → IO Unit
+run fn = do
+  printLn fn
+  text <- readFile fn
+  let xs = parse text
+  let p1 = part1 xs
+  printLn "part1 \{show p1}"
+  let p2 = part2 xs
+  printLn "part2 \{show p2}"
+
+main : IO Unit
+main = do
+  run "aoc2025/day1/eg.txt"
+  run "aoc2025/day1/input.txt"

aoc2025/DayXX.newt

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+module DayXX
+
+import Prelude
+import Node
+import Aoc
+
+run : String → IO Unit
+
+main : IO Unit
+main = do
+  run "aoc2025/dayXX/eg.txt"
+  run "aoc2025/dayXX/input.txt"

aoc2025/Node.newt

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+module Node
+
+import Prelude
+
+pfunc fs : JSObject := `require('fs')`
+pfunc getArgs : List String := `arrayToList(String, process.argv)`
+pfunc readFile uses (MkIORes) : (fn : String) -> IO String := `(fn) => (w) => Prelude_MkIORes(require('fs').readFileSync(fn, 'utf8'), w)`

aoc2025/Prelude.newt

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+../src/Prelude.newt

aoc2025/day1/eg.txt

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+L68
+L30
+R48
+L5
+R60
+L55
+L1
+L99
+R14
+L82

aoc2025/mkday

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+#!/bin/zsh -e
+day=$1
+if [ ! -d day${day} -a ! -z "$1" ]; then
+  echo Make Day ${day}
+  mkdir day${day}
+  sed "s/XX/$day/g" DayXX.newt > Day$day.newt
+fi