Add day 1 part 2

2023/1-1.nix

@@ -1,6 +1,6 @@
 { lib, input }:
 
-with lib; with builtins; let
+with builtins; with lib; rec {
   lines = splitString "\n" input;
 
   linesChars = map (splitString "") lines;
@@ -14,4 +14,4 @@ with lib; with builtins; let
   sumOfLinesNumbers = foldl' add 0 (map fromJSON linesNumbers);
 
   result = sumOfLinesNumbers;
-in result
+}

2023/1-2.nix

@@ -0,0 +1,42 @@
+{ lib, input }:
+
+with builtins; with lib; rec {
+  digits = {
+    zero  = "0";
+    one   = "1";
+    two   = "2";
+    three = "3";
+    four  = "4";
+    five  = "5";
+    six   = "6";
+    seven = "7";
+    eight = "8";
+    nine  = "9";
+  };
+
+  toDigit = maybeDigit: if digits ? "${maybeDigit}" then
+    digits.${maybeDigit}
+  else
+    maybeDigit;
+
+  allNeedles = flatten (mapAttrsToList (key: value: [ key (toString value) ]) digits); 
+  allNeedlesReverse = map reverseString allNeedles;
+
+  reverseString = string: concatStrings (reverseList (stringToCharacters string));
+
+  firstMatch = haystack: needles: let
+      prefixNeedle = findFirst (needle: hasPrefix needle haystack) null needles;
+    in if prefixNeedle != null then
+      prefixNeedle
+    else
+      firstMatch (substring 1 (stringLength haystack - 1) haystack) needles;
+
+  firstLast = line: let
+    first = firstMatch line allNeedles;
+    last = reverseString (firstMatch (reverseString line) allNeedlesReverse);
+  in fromJSON (toDigit first + toDigit last);
+
+  lines = splitString "\n" input;
+
+  result = foldl' add 0 (map firstLast lines);
+}

flake.nix

@@ -10,14 +10,15 @@
   outputs = { nixpkgs, ... }: let
     lib = nixpkgs.lib;
 
-    pathToResult = path: import ./${path}.nix {
+    pathToResult = path: (import ./${path}.nix {
       inherit lib;
 
       input = builtins.concatStringsSep "\n"
         (builtins.filter (line: line != "")
           (lib.splitString "\n" (builtins.readFile ./${path}.in)));
-    };
+    }).result;
   in lib.genAttrs [
     "2023/1-1"
+    "2023/1-2"
   ] pathToResult;
 }