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Implement 2025 day 1 part 2

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Bert Peters
2025-12-01 20:47:21 +01:00
parent 1dc59c18eb
commit 1468c87347
1 changed files with 20 additions and 14 deletions
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32
2025/day01/solve.nix
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@@ -4,28 +4,34 @@
data = builtins.readFile input_file;
lines = builtins.filter (s: s != "" && builtins.isString s) (builtins.split "\n" data);
# Basic maths because the standard library doesn't have it
mod = a: b: a - (a / b) * b;
abs = n: if n < 0 then -n else n;
recurse = list: position:
recurse = list: position: score1: score2:
let
first = builtins.head list;
# This is not guaranteed to work but it does
# This is not guaranteed to work but it's good enough
num_part = builtins.substring 1 999 first;
num = builtins.fromJSON num_part;
next = if (builtins.substring 0 1 first) == "R"
then
position + num
else
position - num;
delta = mod (if (builtins.substring 0 1 first) == "R" then num else -num) 100;
next = mod (position + delta + 100) 100;
new_position = mod ((mod next 100) + 100) 100;
score = if next == 0 then 1 else 0;
circles = num / 100;
score = if new_position == 0 then 1 else 0;
in
if list == [] then
passed = if position == 0 then
0
else
score + (recurse (builtins.tail list) new_position);
if delta < 0 && delta + position <= 0 || delta > 0 && delta + position >= 100 then
1
else
0;
in
recurse lines 50;
if list == [] then
[score1 score2]
else
recurse (builtins.tail list) next (score + score1) (score2 + passed + circles);
in
recurse lines 50 0 0;
}