Day ten part 1

day-10-haskell/.gitignore

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+.stack-work/
+*~

day-10-haskell/Setup.hs

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+import Distribution.Simple
+main = defaultMain

day-10-haskell/app/Main.hs

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+module Main (main) where
+
+import System.Environment.Blank ( getArgs )
+import Task1 (task1)
+
+main :: IO ()
+main = do
+  args <- getArgs
+  case args of
+    ["1", file] -> do
+      input <- readFile file
+      result <- task1 input
+      print result
+    _ -> error "Usage: <1|2> <input file>"

day-10-haskell/day10-haskell.cabal

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+cabal-version: 2.2
+
+-- This file has been generated from package.yaml by hpack version 0.37.0.
+--
+-- see: https://github.com/sol/hpack
+
+name:           day10-haskell
+version:        0.1.0.0
+homepage:       https://github.com/githubuser/day10-haskell#readme
+bug-reports:    https://github.com/githubuser/day10-haskell/issues
+author:         Author name here
+maintainer:     example@example.com
+copyright:      2024 Author name here
+license:        BSD-3-Clause
+build-type:     Simple
+
+source-repository head
+  type: git
+  location: https://github.com/githubuser/day10-haskell
+
+library
+  exposed-modules:
+      Common
+      Task1
+  hs-source-dirs:
+      src
+  ghc-options: -Wall -Wcompat -Widentities -Wincomplete-record-updates -Wincomplete-uni-patterns -Wmissing-home-modules -Wpartial-fields -Wredundant-constraints
+  build-depends:
+      base >=4.7 && <5
+    , containers
+    , flow
+  default-language: Haskell2010
+
+executable day10-haskell-exe
+  main-is: Main.hs
+  hs-source-dirs:
+      app
+  ghc-options: -Wall -Wcompat -Widentities -Wincomplete-record-updates -Wincomplete-uni-patterns -Wmissing-home-modules -Wpartial-fields -Wredundant-constraints -threaded -rtsopts -with-rtsopts=-N
+  build-depends:
+      base >=4.7 && <5
+    , day10-haskell
+  default-language: Haskell2010
+
+test-suite day10-haskell-test
+  type: exitcode-stdio-1.0
+  main-is: Spec.hs
+  hs-source-dirs:
+      test
+  ghc-options: -Wall -Wcompat -Widentities -Wincomplete-record-updates -Wincomplete-uni-patterns -Wmissing-home-modules -Wpartial-fields -Wredundant-constraints -threaded -rtsopts -with-rtsopts=-N
+  build-depends:
+      base >=4.7 && <5
+    , day10-haskell
+  default-language: Haskell2010

day-10-haskell/package.yaml

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+name:                day10-haskell
+version:             0.1.0.0
+github:              "githubuser/day10-haskell"
+license:             BSD-3-Clause
+author:              "Author name here"
+maintainer:          "example@example.com"
+copyright:           "2024 Author name here"
+spec-version:        0.36.0
+
+dependencies:
+- base >= 4.7 && < 5
+
+ghc-options:
+- -Wall
+- -Wcompat
+- -Widentities
+- -Wincomplete-record-updates
+- -Wincomplete-uni-patterns
+- -Wmissing-home-modules
+- -Wpartial-fields
+- -Wredundant-constraints
+
+library:
+  source-dirs: src
+  dependencies:
+  - flow
+  - containers
+
+executables:
+  day10-haskell-exe:
+    main:                Main.hs
+    source-dirs:         app
+    ghc-options:
+    - -threaded
+    - -rtsopts
+    - -with-rtsopts=-N
+    dependencies:
+    - day10-haskell
+
+tests:
+  day10-haskell-test:
+    main:                Spec.hs
+    source-dirs:         test
+    ghc-options:
+    - -threaded
+    - -rtsopts
+    - -with-rtsopts=-N
+    dependencies:
+    - day10-haskell

day-10-haskell/src/Common.hs

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+module Common where
+
+import Control.Monad (join)
+import Text.Read (readMaybe)
+import Flow
+
+type WorldMap = [[Maybe Int]]
+type Position = (Int, Int)
+
+parseMap :: String -> WorldMap
+parseMap input = lines input >>= pure . map readTile
+  where
+    readTile :: Char -> Maybe Int
+    readTile c = readMaybe [c]
+
+findInMap :: Int -> WorldMap -> [Position]
+findInMap _ [] = []
+findInMap needle haystack = enumerate haystack |> map (\(y, line) -> findInLine (0, y) line) |> join
+  where
+    enumerate = zip [0..]
+    findInLine :: Position -> [Maybe Int] -> [Position]
+    findInLine _ [] = []
+    findInLine pos@(x, y) ((Just element):rest)
+      | element == needle = pos : findInLine (x+1, y) rest
+      | otherwise = findInLine (x+1, y) rest
+    findInLine (x, y) (Nothing:rest) = findInLine (x+1, y) rest
+

day-10-haskell/src/Task1.hs

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+module Task1 (task1) where
+
+import Common
+import Data.List ((!?))
+import qualified Data.Set as Set
+import Control.Monad (join)
+import Flow
+
+task1 :: String -> IO Int
+task1 input = let worldMap = parseMap input
+                  trailheads = findInMap 0 worldMap
+              in trailheads >>= followToHills worldMap |> map length |> sum |> return
+  where
+    followToHills :: WorldMap -> Position -> [Position]
+    followToHills worldMap trailhead = followAllUp 0 [trailhead]
+      where
+        followAllUp :: Int -> [Position] -> [Position]
+        followAllUp 9 positions = positions
+        followAllUp height positions = positions |> map followUp |> join |> Set.fromList |> Set.toList |> followAllUp (height + 1)
+          where
+            followUp :: Position -> [Position]
+            followUp pos = [(0, -1), (-1, 0), (0, 1), (1, 0)] |> map (offset pos) |> filter canGoUp
+
+            canGoUp :: Position -> Bool
+            canGoUp (x, y) = case worldMap !? y of
+              Nothing -> False
+              Just line -> case line !? x of
+                Nothing -> False
+                Just Nothing -> False
+                Just (Just element) -> element == height + 1
+
+    offset :: Position -> Position -> Position
+    offset (x1, y1) (x2, y2) = (x1 + x2, y1 + y2)

day-10-haskell/stack.yaml

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+# This file was automatically generated by 'stack init'
+#
+# Some commonly used options have been documented as comments in this file.
+# For advanced use and comprehensive documentation of the format, please see:
+# https://docs.haskellstack.org/en/stable/yaml_configuration/
+
+# A 'specific' Stackage snapshot or a compiler version.
+# A snapshot resolver dictates the compiler version and the set of packages
+# to be used for project dependencies. For example:
+#
+# snapshot: lts-22.28
+# snapshot: nightly-2024-07-05
+# snapshot: ghc-9.6.6
+#
+# The location of a snapshot can be provided as a file or url. Stack assumes
+# a snapshot provided as a file might change, whereas a url resource does not.
+#
+# snapshot: ./custom-snapshot.yaml
+# snapshot: https://example.com/snapshots/2024-01-01.yaml
+snapshot:
+  url: https://raw.githubusercontent.com/commercialhaskell/stackage-snapshots/master/lts/23/0.yaml
+
+# User packages to be built.
+# Various formats can be used as shown in the example below.
+#
+# packages:
+# - some-directory
+# - https://example.com/foo/bar/baz-0.0.2.tar.gz
+#   subdirs:
+#   - auto-update
+#   - wai
+packages:
+- .
+# Dependency packages to be pulled from upstream that are not in the snapshot.
+# These entries can reference officially published versions as well as
+# forks / in-progress versions pinned to a git hash. For example:
+#
+# extra-deps:
+# - acme-missiles-0.3
+# - git: https://github.com/commercialhaskell/stack.git
+#   commit: e7b331f14bcffb8367cd58fbfc8b40ec7642100a
+#
+# extra-deps: []
+
+# Override default flag values for project packages and extra-deps
+# flags: {}
+
+# Extra package databases containing global packages
+# extra-package-dbs: []
+
+# Control whether we use the GHC we find on the path
+# system-ghc: true
+#
+# Require a specific version of Stack, using version ranges
+# require-stack-version: -any # Default
+# require-stack-version: ">=3.1"
+#
+# Override the architecture used by Stack, especially useful on Windows
+# arch: i386
+# arch: x86_64
+#
+# Extra directories used by Stack for building
+# extra-include-dirs: [/path/to/dir]
+# extra-lib-dirs: [/path/to/dir]
+#
+# Allow a newer minor version of GHC than the snapshot specifies
+# compiler-check: newer-minor

day-10-haskell/stack.yaml.lock

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+# This file was autogenerated by Stack.
+# You should not edit this file by hand.
+# For more information, please see the documentation at:
+#   https://docs.haskellstack.org/en/stable/lock_files
+
+packages: []
+snapshots:
+- completed:
+    sha256: 9444fadfa30b67a93080254d53872478c087592ad64443e47c546cdcd13149ae
+    size: 678857
+    url: https://raw.githubusercontent.com/commercialhaskell/stackage-snapshots/master/lts/23/0.yaml
+  original:
+    url: https://raw.githubusercontent.com/commercialhaskell/stackage-snapshots/master/lts/23/0.yaml

day-10-haskell/test/Spec.hs

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+main :: IO ()
+main = putStrLn "Test suite not yet implemented"