advent of code 2025 in ts and nix
dunkirk.sh
1let
2 input = builtins.readFile ../../shared/01/input.txt;
3 lines = builtins.filter (s: builtins.isString s && s != "") (builtins.split "\n" input);
4
5 mod = a: b: a - (a / b) * b;
6
7 part1 =
8 let
9 processLine = state: line:
10 let
11 dir = builtins.substring 0 1 line == "R";
12 num = builtins.fromJSON (builtins.substring 1 (builtins.stringLength line - 1) line);
13 newDial = mod (if dir then state.dial + num else state.dial - num + 100) 100;
14 in {
15 dial = newDial;
16 count = state.count + (if newDial == 0 then 1 else 0);
17 };
18
19 result = builtins.foldl' processLine { dial = 50; count = 0; } lines;
20 in result.count;
21
22 part2 =
23 let
24 processLine = state: line:
25 let
26 dir = builtins.substring 0 1 line;
27 num = builtins.fromJSON (builtins.substring 1 (builtins.stringLength line - 1) line);
28 dialBefore = state.dial;
29
30 distToZero =
31 let raw = if dir == "R" then mod (100 - dialBefore) 100 else mod dialBefore 100;
32 in if raw == 0 then 100 else raw;
33
34 passCount = if num >= distToZero then 1 + (num - distToZero) / 100 else 0;
35
36 newDial =
37 let d = if dir == "R"
38 then mod (dialBefore + num) 100
39 else mod (100 + dialBefore - (mod num 100)) 100;
40 in mod (100 + d) 100;
41 in {
42 dial = newDial;
43 count = state.count + passCount;
44 };
45
46 result = builtins.foldl' processLine { dial = 50; count = 0; } lines;
47 in result.count;
48
49in {
50 inherit part1 part2;
51}