day 2 part 1

2025/day_2.nix

@@ -0,0 +1,51 @@
+# nix eval -f ./day_2.nix part1
+# nix eval -f ./day_2.nix part1 --arg input 'builtins.readFile ./puzzle_cache/day_2_1'
+# nix eval -f ./day_2.nix part2
+# nix eval -f ./day_2.nix part2 --arg input 'builtins.readFile ./puzzle_cache/day_2_1'
+{
+  input ? (builtins.readFile ./puzzle_cache/day_2_0),
+}:
+with builtins;
+with import ./utils.nix;
+let
+  # reversedChars =
+  #   str:
+  #   let
+  #     len = length str;
+  #   in
+  #   builtins.genList (i: builtins.elemAt str (len - 1 - i)) len;
+  isStrPatternSplit =
+    str:
+    let
+      strLen = stringLength str;
+    in
+    (
+      if mod strLen 2 == 0 then
+        let
+          half = strLen / 2;
+          firstHalf = substring 0 half str;
+          secondHalf = substring half strLen str;
+          # secondReversed = reversedChars secondHalf;
+        in
+        firstHalf == secondHalf
+      else
+        false
+    );
+
+  ranges = map (range: map (v: toIntBase10 v) (split "-" range)) (split "," input);
+  fullRanges = map (itr: map (v: toString v) (rangeInclusive (elemAt itr 0) (elemAt itr 1))) ranges;
+  invalidIds = flatten (
+    map (
+      range:
+      (reduce (
+        invalidIds: id: invalidIds ++ (if isStrPatternSplit id then [ id ] else [ ])
+      ) [ ] range)
+    ) fullRanges
+  );
+  invalidIdNums = map (v: toIntBase10 v) invalidIds;
+  invalidIdSum = sum invalidIdNums;
+in
+{
+  part1 = invalidIdSum;
+  part2 = 0;
+}