day 2

day2/default.nix

@@ -0,0 +1,13 @@
+{ lib, utils, ... }:
+with lib;
+with builtins;
+with utils;
+let
+  records = map (l: map toInt (splitWhitespace l)) (readLines ./input);
+  getMaxDelta = l: (foldl' (prev: value: { inherit value; maxDelta = max prev.maxDelta (delta prev.value value); } ) { value = head l; maxDelta = 0; } l).maxDelta;
+  isSafe = r: let sorted = sort lessThan r; in (r == sorted || r == (reverseList sorted)) && allUnique r && (3 >= getMaxDelta r);
+  isSafeDampened = r: any isSafe ([ r ] ++ (map (deleteAt r) (range 0 (length r))));
+in {
+  part1 = count isSafe records;
+  part2 = count isSafeDampened records;
+}

utils.nix

@@ -1,10 +1,12 @@
 { lib, ... }:
 with lib;
 with builtins; rec {
-  readLines = f: let lines = filter isString (split "\n" (readFile f)); in take ((length lines) - 1) lines;
+  readLines = f: init (filter isString (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);
   listSum = foldl' add 0;
+  deleteAt = l: i: (take i l) ++ (drop (i+1) l);
   eq = x: y: x == y;
+  greaterThan = x: y: x > y;
 }