Day 6: Wait For It

README.md

@@ -10,4 +10,4 @@ Development occurs in language-specific directories:
 |[Day3.hs](hs/src/Day3.hs)|[Day3.kt](kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Day3.kt)|[day3.py](py/aoc2023/day3.py)|[day3.rs](rs/src/day3.rs)|
 |[Day4.hs](hs/src/Day4.hs)|[Day4.kt](kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Day4.kt)|[day4.py](py/aoc2023/day4.py)|[day4.rs](rs/src/day4.rs)|
 |[Day5.hs](hs/src/Day5.hs)|[Day5.kt](kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Day5.kt)|[day5.py](py/aoc2023/day5.py)|[day5.rs](rs/src/day5.rs)|
-||[Day6.kt](kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Day6.kt)|||
+|[Day6.hs](hs/src/Day6.hs)|[Day6.kt](kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Day6.kt)|||

hs/aoc2023.cabal

@@ -25,7 +25,8 @@ library
         Day2,
         Day3,
         Day4,
-        Day5
+        Day5,
+        Day6
 
     -- Modules included in this library but not exported.
     other-modules:
@@ -75,7 +76,8 @@ test-suite aoc2023-test
         Day2Spec,
         Day3Spec,
         Day4Spec,
-        Day5Spec
+        Day5Spec,
+        Day6Spec
     build-depends:
         aoc2023,
         base ^>=4.17.2.0,

hs/app/Main.hs

@@ -6,6 +6,7 @@ import qualified Day2 (part1, part2)
 import qualified Day3 (part1, part2)
 import qualified Day4 (part1, part2)
 import qualified Day5 (part1, part2)
+import qualified Day6 (part1, part2)
 
 import Control.Monad (ap, when)
 import Data.Foldable (find)
@@ -40,3 +41,4 @@ main = do
     run 3 print [Day3.part1, Day3.part2]
     run 4 (either fail print) [Day4.part1, Day4.part2]
     run 5 (either (fail . errorBundlePretty) print) [Day5.part1, Day5.part2]
+    run 6 (either fail print) [pure . Day6.part1, Day6.part2]

hs/bench/Main.hs

@@ -10,6 +10,7 @@ import qualified Day2 (part1, part2)
 import qualified Day3 (part1, part2)
 import qualified Day4 (part1, part2)
 import qualified Day5 (part1, part2)
+import qualified Day6 (part1, part2)
 import System.Environment (lookupEnv)
 import System.FilePath (combine)
 
@@ -40,4 +41,8 @@ main = defaultMain
       [ bench "part 1" $ nf Day5.part1 input
       , bench "part 2" $ nf Day5.part2 input
       ]
+  , env (getDayInput 6) $ \input -> bgroup "Day 6"
+      [ bench "part 1" $ nf Day6.part1 input
+      , bench "part 2" $ nf Day6.part2 input
+      ]
   ]

hs/src/Day6.hs

@@ -0,0 +1,29 @@
+{-|
+Module:         Day6
+Description:    <https://adventofcode.com/2023/day/6 Day 6: Wait For It>
+-}
+{-# LANGUAGE OverloadedStrings #-}
+module Day6 (part1, part2) where
+
+import Common (readEntire)
+import Data.Char (isDigit)
+import Data.Function (on)
+import Data.List (unfoldr)
+import Data.Text (Text)
+import qualified Data.Text as T (breakOn, dropWhile, filter)
+import qualified Data.Text.Read as T (decimal)
+
+winCount :: Int -> Int -> Int
+winCount time distance = ceiling (b + d - 1) - floor (b - d + 1) + 1 where
+    b = fromIntegral time / 2
+    d = sqrt $ b * b - fromIntegral distance
+
+part1 :: Text -> Int
+part1 = product . uncurry (zipWith winCount `on` unfoldr reader) . T.breakOn "\n"
+  where reader = either (const Nothing) Just . T.decimal . T.dropWhile (not . isDigit)
+
+part2 :: Text -> Either String Int
+part2 input = winCount <$>
+    readEntire T.decimal (T.filter isDigit line1) <*>
+    readEntire T.decimal (T.filter isDigit line2)
+  where (line1, line2) = T.breakOn "\n" input

hs/test/Day6Spec.hs

@@ -0,0 +1,22 @@
+{-# LANGUAGE OverloadedStrings #-}
+module Day6Spec (spec) where
+
+import Data.Text (Text)
+import qualified Data.Text as T (unlines)
+import Day6 (part1, part2)
+import Test.Hspec (Spec, describe, it, shouldBe)
+
+example :: Text
+example = T.unlines
+  [ "Time:      7  15   30"
+  , "Distance:  9  40  200"
+  ]
+
+spec :: Spec
+spec = do
+    describe "part 1" $ do
+        it "examples" $ do
+            part1 example `shouldBe` 288
+    describe "part 2" $ do
+        it "examples" $ do
+            part2 example `shouldBe` Right 71503