2025 day 2

2025/day_1.nix

@@ -1,12 +1,13 @@
-# nix eval -f ./day_1.nix countZero
+# nix eval -f ./day_1.nix part1
-# nix eval -f ./day_1.nix countZero --arg input 'builtins.readFile ./puzzle_cache/day_1_1'
+# nix eval -f ./day_1.nix part1 --arg input 'builtins.readFile ./puzzle_cache/day_1_1'
+# nix eval -f ./day_1.nix part2
+# nix eval -f ./day_1.nix part2 --arg input 'builtins.readFile ./puzzle_cache/day_1_1'
 {
   input ? (builtins.readFile ./puzzle_cache/day_1_0),
 }:
+with builtins;
+with import ./utils.nix;
 let
-  utils = import ./utils.nix;
-  inherit (utils) toIntBase10 mod;
-
   # Split into non-empty lines
   lines = builtins.filter (s: builtins.isString s && s != "") (builtins.split "\n" input);
 
@@ -18,6 +19,15 @@ let
 
   rotations = map parseLine lines;
 
+  countZerosDuring =
+    position: dir: dist:
+    if dir == "R" then
+      floor ((position + dist) / 100.0) - floor (position / 100.0)
+    else if dir == "L" then
+      floor ((position -1) / 100.0) - floor ((position - dist - 1) / 100.0)
+    else
+      builtins.throw "Invalid direction: ${dir}";
+
   # Fold over the list to simulate the dial
   step =
     state: rot:
@@ -29,19 +39,23 @@ let
           mod (state.position + rot.dist) 100
         else
           builtins.trace "Invalid direction: ${rot.dir}" state.position;
+      countZeroPassed = state.countZeroPassed + (countZerosDuring state.position rot.dir rot.dist);
       countZero = state.countZero + (if position == 0 then 1 else 0);
     in
     {
-      inherit position countZero;
+      inherit position countZero countZeroPassed;
     };
 
   initialState = {
     position = 50;
     countZero = 0;
+    countZeroPassed = 0;
   };
 
   finalState = builtins.foldl' step initialState rotations;
 in
 {
-  inherit (finalState) position countZero;
+  part1 = finalState.countZero;
+  part2 = finalState.countZeroPassed;
+  # 6689 should be part 2
 }

2025/utils.nix

@@ -1,4 +1,6 @@
 {
   toIntBase10 = str: builtins.fromJSON "${str}";
   mod = a: b: a - b * (builtins.floor (a / b));
+  min = a: b: if a < b then a else b;
+  max = a: b: if a > b then a else b;
 }