isaaccorbrey.com
Advent of Code for 2025!
day 1: Access the secret entrance
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examples/day_01_secret_entrance.proptest-regressions
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examples/day_01_secret_entrance.proptest-regressions
···
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# Seeds for failure cases proptest has generated in the past. It is
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# automatically read and these particular cases re-run before any
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# novel cases are generated.
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#
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# It is recommended to check this file in to source control so that
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# everyone who runs the test benefits from these saved cases.
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cc 49c016dc4fd11fa9bbfb8bbf0f07e752bc534c486ad5b54b7bb24b97f083aab4 # shrinks to s = ":"
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cc 8492ad45bd0ba7b1c687c413c52779c63bb91de1c2ec36d4c5e58cffdeb07e9c # shrinks to s = "R2200000000"
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cc 99935ba16841a9db1a7e192bec5734770069262016d0e91724af515fdd5fb798 # shrinks to acc = 0, delta = 0
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cc 406bf951122ca7019f2f56865072c4edf7f09d75c44fab42846bcea9cbb6278a # shrinks to acc = 16, delta = -6916
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examples/day_01_secret_entrance.rs
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examples/day_01_secret_entrance.rs
···
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fn main() {
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aoc2025::run(
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"Day 1: Secret Entrance",
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"inputs/day_01.txt",
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parse_input,
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part_1,
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part_2,
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)
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.unwrap();
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}
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/// Parses the input into a list of signed integers.
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fn parse_input(input: &str) -> Vec<i32> {
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input
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.split('\n')
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.filter(|x| !x.is_empty())
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.filter_map(|x| parse_line(x))
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.collect()
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}
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/// Parses the given line into a signed integer
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fn parse_line(line: &str) -> Option<i32> {
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let line = line.replace("L", "-").replace("R", "");
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i32::from_str_radix(line.as_str(), 10).ok()
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}
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fn part_1(deltas: Vec<i32>) -> usize {
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// The input file contains a list of rotations in the form `XYY`,
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// where `X` is a direction (`L` for left or `R` for right) and
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// `YY` is a non-zero-padded number of clicks.
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//
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// The dial consists of numbers 0-99. Turning left decreases the
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// number, and turning right increases it. Turning too far will
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// overflow to the opposite end of the range.
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//
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// The dial starts at 50. Run the input file against this dial and
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// record the number of times it leaves it pointing at 0.
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// Iterate through the list and count the number of times the
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// accumulated sum equals zero.
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(deltas.into_iter())
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.scan(50, |position, delta| {
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*position += delta;
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Some(*position)
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})
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.filter(|position| position % 100 == 0)
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.count()
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}
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fn part_2(deltas: Vec<i32>) -> i32 {
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(deltas.into_iter())
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.scan(50, |prev, delta| {
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let (next, hits) = step(*prev, delta);
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*prev = next;
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Some(hits)
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})
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.sum()
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}
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fn step(start: i32, delta: i32) -> (i32, i32) {
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let mut hits = (delta / 100).abs();
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let remainder = delta % 100;
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if start + remainder <= 0 && start != 0 || 99 < start + remainder {
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hits += 1;
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}
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((start + delta).rem_euclid(100), hits)
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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use proptest::prelude::*;
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prop_compose! {
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fn line_input()(s in -999_i32..999) -> (i32, String) {
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(s, format!("{}{}", if s < 0 { "L" } else { "R" }, s.abs()))
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}
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}
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mod parse_line {
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use super::*;
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#[test]
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fn ignores_gibberish() {
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assert_eq!(None, parse_line(":"));
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}
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proptest! {
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#[test]
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fn doesnt_crash(s in "\\PC*") {
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parse_line(&s);
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}
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#[test]
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fn parses_lines_correctly((s, line) in line_input()) {
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prop_assert_eq!(s, parse_line(&line).unwrap())
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}
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}
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}
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mod parse_input {
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use super::*;
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proptest! {
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#[test]
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fn doesnt_crash(s in "\\PC+") {
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parse_input(&s);
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}
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#[test]
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fn ignores_empty_lines(s in "\\n+") {
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prop_assert!(parse_input(&s).is_empty());
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}
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#[test]
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fn parses_files(s in prop::collection::vec(line_input(), 1..100)) {
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let (values, input): (Vec<i32>, Vec<String>) = s.into_iter().unzip();
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prop_assert_eq!(values, parse_input(&input.join("\n")));
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}
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}
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}
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mod part_1 {
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use super::*;
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proptest! {
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#[test]
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fn counts_halfstep_deltas(s in prop::collection::vec(Just(50_i32), 0..100)) {
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prop_assert_eq!((s.len() + 1) / 2, part_1(s));
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}
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}
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}
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mod part_2 {
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use super::*;
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// Slow, naive step implementation to compare fast version against.
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fn step_reference(start: i32, delta: i32) -> (i32, i32) {
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let mut pos = start;
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let dir = if delta >= 0 { 1 } else { -1 };
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let mut hits = 0;
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for _ in 0..delta.abs() {
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pos += dir;
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if pos.rem_euclid(100) == 0 {
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hits += 1;
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}
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}
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let final_acc = pos.rem_euclid(100);
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(final_acc, hits)
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}
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proptest! {
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#[test]
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fn counts_perfect_deltas(s in prop::collection::vec(Just(100), 0..100)) {
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prop_assert_eq!(s.len() as i32, part_2(s));
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}
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#[test]
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fn counts_perfect_multiple_deltas(s in prop::collection::vec(0..9, 0..100)) {
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prop_assert_eq!(
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s.clone().into_iter().sum::<i32>(),
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part_2(s.into_iter().map(|x| x * 100).collect())
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);
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}
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#[test]
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fn steps_correctly(
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start in 0i32..100,
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delta in -10_000_i32..-1
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) {
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let reference_hits = step_reference(start, delta);
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let real_hits = step(start, delta);
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prop_assert_eq!(reference_hits, real_hits);
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}
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}
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}
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}