commit 4f3ad6d9209dada1f41fc3f14cdca11f648b1a46
Author: Grimmauld <Grimmauld@grimmauld.de>
Date:   Sun Dec 1 15:50:11 2024 +0100

    day 1

diff --git a/README.md b/README.md
new file mode 100644
index 0000000..2b633d3
--- /dev/null
+++ b/README.md
@@ -0,0 +1 @@
+To evaluate a certain day, just run `nix eval .#day1`
diff --git a/day1/default.nix b/day1/default.nix
new file mode 100644
index 0000000..f87383e
--- /dev/null
+++ b/day1/default.nix
@@ -0,0 +1,12 @@
+{ lib, utils, ... }:
+with lib;
+with builtins;
+with utils;
+let
+  numbers = map (l: map toInt (splitWhitespace l)) (readLines ./input);
+  left = sortOn noop (map (flip elemAt 0) numbers);
+  right = sortOn noop (map (flip elemAt 1) numbers);
+in {
+  part1 = listSum (zipListsWith delta left right);
+  part2 = listSum (map (x: x * (count (y: x == y) right)) left);
+}
diff --git a/day1/input b/day1/input
new file mode 100644
index 0000000..863e4f7
--- /dev/null
+++ b/day1/input
@@ -0,0 +1,1000 @@
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diff --git a/flake.lock b/flake.lock
new file mode 100644
index 0000000..a0a823d
--- /dev/null
+++ b/flake.lock
@@ -0,0 +1,27 @@
+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1733038015,
+        "narHash": "sha256-kIKqS3093Xz5vuvSLk0x1hqo2pFaGwMjnwr3qrTBkzk=",
+        "owner": "nixos",
+        "repo": "nixpkgs",
+        "rev": "767b0e3398fb899d0c88a9f7aecf30dd1cad3166",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nixos",
+        "ref": "nixos-unstable-small",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}
diff --git a/flake.nix b/flake.nix
new file mode 100644
index 0000000..7c2e4c5
--- /dev/null
+++ b/flake.nix
@@ -0,0 +1,17 @@
+{
+  description = "Advent of Code 2024, but Nix";
+
+  inputs = { nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable-small"; };
+
+  outputs = { self, nixpkgs }:
+    let
+      inherit (nixpkgs) lib;
+      utils = import ./utils.nix { inherit lib nixpkgs; };
+    in {
+      formatter.x86_64-linux = nixpkgs.legacyPackages.x86_64-linux.nixfmt;
+    } // (builtins.mapAttrs
+      (n: v: import "${./.}/${n}" { inherit lib nixpkgs utils; })
+      (lib.filterAttrs (n: v:
+        v == "directory" && (builtins.match "(day[[:digit:]]+)" n) != null)
+        (builtins.readDir ./.)));
+}
diff --git a/utils.nix b/utils.nix
new file mode 100644
index 0000000..0dae919
--- /dev/null
+++ b/utils.nix
@@ -0,0 +1,10 @@
+{ lib, ... }:
+with lib;
+with builtins; rec {
+  readLines = f: filter (s: (isString s) && s != "") (split "\n" (readFile f));
+  splitWhitespace = s: filter isString (builtins.split "[[:space:]]+" s);
+  abs = i: if i >= 0 then i else i * -1;
+  delta = x: y: abs (x - y);
+  noop = x: x;
+  listSum = foldl' add 0;
+}