day 1

Signed-off-by: Amneesh Singh <natto@weirdnatto.in>

.envrc

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+use flake

.gitignore

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+dist*
+inputs/*.in
+result
+*~

README.md

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+[haskell-flake](https://github.com/srid/haskell-flake)
+
+Copied from: https://github.com/srid/haskell-flake/tree/0.4.0/example
+
+[Documentation](https://zero-to-flakes.com/haskell-flake/)
+

aoc2024.cabal

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+cabal-version: 3.0
+name:          aoc2024
+version:       0.1.0.0
+license:       BSD-3-Clause
+author:        Amneesh
+maintainer:    natto@weirdnatto.in
+build-type:    Simple
+
+common common
+  ghc-options:   -Wall -O3
+  build-depends:
+    , base    >=4.14 && <5
+    , parsec  >=3
+
+library libaoc
+  import:          common
+  exposed:         False
+  hs-source-dirs:  lib
+  build-depends:   containers
+  exposed-modules: AoC
+
+executable p1
+  import:         common
+  hs-source-dirs: src
+  main-is:        P1.hs
+  build-depends:  libaoc

flake.lock

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+{
+  "nodes": {
+    "flake-parts": {
+      "inputs": {
+        "nixpkgs-lib": "nixpkgs-lib"
+      },
+      "locked": {
+        "lastModified": 1730504689,
+        "narHash": "sha256-hgmguH29K2fvs9szpq2r3pz2/8cJd2LPS+b4tfNFCwE=",
+        "owner": "hercules-ci",
+        "repo": "flake-parts",
+        "rev": "506278e768c2a08bec68eb62932193e341f55c90",
+        "type": "github"
+      },
+      "original": {
+        "owner": "hercules-ci",
+        "repo": "flake-parts",
+        "type": "github"
+      }
+    },
+    "haskell-flake": {
+      "locked": {
+        "lastModified": 1732461017,
+        "narHash": "sha256-FS4ZavcceO2GJOKGDejkJsuEngHb2Ioq+jnORGZzaKE=",
+        "owner": "srid",
+        "repo": "haskell-flake",
+        "rev": "725292998cdb695dc312325603a662afa97b9e86",
+        "type": "github"
+      },
+      "original": {
+        "owner": "srid",
+        "repo": "haskell-flake",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1732780316,
+        "narHash": "sha256-NskLIz0ue4Uqbza+1+8UGHuPVr8DrUiLfZu5VS4VQxw=",
+        "owner": "nixos",
+        "repo": "nixpkgs",
+        "rev": "226216574ada4c3ecefcbbec41f39ce4655f78ef",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nixos",
+        "ref": "nixpkgs-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "nixpkgs-lib": {
+      "locked": {
+        "lastModified": 1730504152,
+        "narHash": "sha256-lXvH/vOfb4aGYyvFmZK/HlsNsr/0CVWlwYvo2rxJk3s=",
+        "type": "tarball",
+        "url": "https://github.com/NixOS/nixpkgs/archive/cc2f28000298e1269cea6612cd06ec9979dd5d7f.tar.gz"
+      },
+      "original": {
+        "type": "tarball",
+        "url": "https://github.com/NixOS/nixpkgs/archive/cc2f28000298e1269cea6612cd06ec9979dd5d7f.tar.gz"
+      }
+    },
+    "root": {
+      "inputs": {
+        "flake-parts": "flake-parts",
+        "haskell-flake": "haskell-flake",
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

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+{
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";
+    flake-parts.url = "github:hercules-ci/flake-parts";
+    haskell-flake.url = "github:srid/haskell-flake";
+  };
+  outputs = inputs@{ self, nixpkgs, flake-parts, ... }:
+    flake-parts.lib.mkFlake { inherit inputs; } {
+      systems = nixpkgs.lib.systems.flakeExposed;
+      imports = [ inputs.haskell-flake.flakeModule ];
+
+      perSystem = { self', pkgs, ... }: {
+        haskellProjects.default = {
+          basePackages = pkgs.haskellPackages;
+          devShell = {
+            enable = true;
+            hlsCheck.enable = true;
+
+            tools = hp: {
+              inherit (pkgs)
+                nixpkgs-fmt;
+              inherit (hp)
+                cabal-fmt
+                fourmolu;
+            };
+          };
+        };
+
+        packages.default = self'.packages.aoc2024;
+      };
+    };
+}

fourmolu.yaml

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+indentation: 2
+comma-style: leading
+record-brace-space: true 
+indent-wheres: true
+diff-friendly-import-export: true 
+respectful: true 
+haddock-style: multi-line 
+newlines-between-decls: 1 

lib/AoC.hs

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+module AoC where
+
+import Text.Parsec
+
+extract :: Either ParseError a -> a
+extract (Left err) = error ("Parsing failed: " ++ show err)
+extract (Right val) = val
+
+count :: (Eq a) => a -> [a] -> Int
+count x = length . filter (x ==)

src/P1.hs

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+module Main where
+
+import qualified AoC as A (count, extract)
+import Data.List (sort)
+import Text.Parsec (digit, many1, newline, parse, space, try)
+import Text.Parsec.String (Parser)
+
+parseLists :: Parser ([Int], [Int])
+parseLists =
+  unzip
+    -- multiple lines
+    <$> many1
+      ( (,)
+          -- first number
+          <$> (read <$> many1 digit)
+          -- second number
+          <*> (many1 space *> (read <$> many1 digit) <* try newline)
+      )
+
+part1 :: [Int] -> [Int] -> Int
+part1 xs ys = sum $ zipWith ((abs .) . (-)) xs ys
+
+part2 :: [Int] -> [Int] -> Int
+part2 xs ys = sum $ map (\x -> x * A.count x ys) xs
+
+main :: IO ()
+main =
+  do
+    raw <- readFile "./inputs/p1.in"
+    -- parse the input
+    let (xs', ys') = A.extract $ parse parseLists "" raw
+    -- sort the lists
+    let (xs, ys) = (sort xs', sort ys')
+    putStr "Part 1: " >> print (part1 xs ys)
+    putStr "Part 2: " >> print (part2 xs ys)