2024: init

2024/day02/default.nix

@@ -0,0 +1,40 @@
+{ pkgs, lib }:
+
+with lib;
+
+let
+  input = pipe (fileContents ./input.txt) [
+    (splitString "\n")
+    (map (split "[[:space:]]+"))
+    (map (filter (x: x != [])))
+    (map (map toInt))
+  ];
+
+  # - The levels are either all increasing or all decreasing.
+  # - Any two adjacent levels differ by at least one and at most three.
+  safeCondition = xs: let
+    zipped = zipLists xs (tail xs);
+  in (all ({ fst, snd }: let x = fst - snd; in  1 <= x && x <=  3) zipped)
+  || (all ({ fst, snd }: let x = fst - snd; in -1 >= x && x >= -3) zipped);
+
+  answer1 = lib.pipe input [
+    (filter safeCondition)
+    length
+    toString
+  ];
+
+  answer2 = lib.pipe input [
+    (filter (xs: let
+      variants = genList (i: (take i xs) ++ (drop (i + 1) xs)) (length xs);
+    in any safeCondition variants))
+    length
+    toString
+  ];
+in
+  pkgs.writeText "answers" ''
+  Task1:
+    ${answer1}
+
+  Task2:
+    ${answer2}
+''