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import gleam/io
import gleam/bool
import util/input_util
const mod = 20_201_227
const init_subject = 7
fn forward_transform(value: Int, subject: Int, loop: Int) -> Int {
use <- bool.guard(when: loop == 0, return: value)
forward_transform({ value * subject } % mod, subject, loop - 1)
}
fn backward_transform(value: Int, subject: Int, loop: Int, result: Int) -> Int {
use <- bool.guard(when: value == result, return: loop)
backward_transform({ value * subject } % mod, subject, loop + 1, result)
}
fn find_result(subject: Int, loop: Int) -> Int {
forward_transform(1, subject, loop)
}
fn find_loop(subject: Int, result: Int) -> Int {
backward_transform(1, subject, 0, result)
}
fn part1(keys: List(Int)) -> Int {
let assert [card_key, door_key] = keys
let card_loop = find_loop(init_subject, card_key)
let card_result = find_result(door_key, card_loop)
let door_loop = find_loop(init_subject, door_key)
let door_result = find_result(card_key, door_loop)
let assert True = card_result == door_result
card_result
}
pub fn main() -> Nil {
let testing = input_util.read_numbers("test25")
let assert 14_897_079 = part1(testing)
let input = input_util.read_numbers("day25")
io.debug(part1(input))
Nil
}
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