Year 2016: Day 15

CHANGELOG.md

@@ -10,6 +10,10 @@ Of note:
 - The changelog 2015.5.2 has been rewritten from each commit content.
 - This file may be amended entirely in the future to adhere to the [GNU Changelog style](https://www.gnu.org/prep/standards/html_node/Style-of-Change-Logs.html#Style-of-Change-Logs)
 
+## [2016.15.1]
+### Added
+- Solved [exercice for 2016, day 15](src/year_2016/day_15.rs).
+
 ## [2016.14.1]
 ### Added
 - Solved [exercice for 2016, day 14](src/year_2016/day_14.rs).

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "advent-rs"
-version = "2016.14.1"
+version = "2016.15.1"
 edition = "2021"
 authors = ["Arnaud 'red' Rouyer"]
 readme = "README.md"

NOTES_2016.md

@@ -50,3 +50,23 @@ Looking at it carefully proved very smart: both galenelias and me lost too much
 ## Day 10: Balance Bots
 
 This exercise got me to face the worst part of Rust: iterating over a hashmap while mutating it.
+
+## Day 11: Radioisotope Thermoelectric Generators
+
+Ugh. I hated this just as much as the first time.
+
+## Day 12: Leonardo's Monorail
+
+Finally, we are back into interesting exercises!
+
+## Day 13: A Maze of Twisty Little Cubicles
+
+...
+
+## Day 14: One-Time Pad
+
+Computing MD5 hashes is never interesting.
+
+## Day 15: Timing is Everything
+
+Finally, something funny to do.

README.md

@@ -6,7 +6,7 @@ As I said, [Consistency is hard](https://github.com/joshleaves/advent-rb), and I
 
 I'm also adding notes that may be useful if you're (like me) discovering Rust:
 - [2015, complete!](NOTES_2015.md)
-- [2016, up to day 14](NOTES_2016.md)
+- [2016, up to day 15](NOTES_2016.md)
 
 # Regarding style rules
 I'm gonna use a mix of what `cargo fmt` does, with some stuff that feels more natural to me.

benches/year_2016.rs

@@ -12,6 +12,7 @@ use advent_rs::year_2016::day_11;
 use advent_rs::year_2016::day_12;
 use advent_rs::year_2016::day_13;
 use advent_rs::year_2016::day_14;
+use advent_rs::year_2016::day_15;
 use criterion::{black_box, criterion_group, criterion_main, Criterion};
 
 pub fn year_2016_day_01(c: &mut Criterion) {
@@ -182,6 +183,18 @@ pub fn year_2016_day_14(c: &mut Criterion) {
   g2016_day_14.finish();
 }
 
+pub fn year_2016_day_15(c: &mut Criterion) {
+  let mut g2016_day_15 = c.benchmark_group("year_2016::day_15");
+  let input_year_2016_day_15 = include_str!("../inputs/year_2016/day_15_input");
+  g2016_day_15.bench_function("year_2016::day_15_v1", |b| {
+    b.iter(|| day_15::day_15_v1(black_box(input_year_2016_day_15)))
+  });
+  g2016_day_15.bench_function("year_2016::day_15_v2", |b| {
+    b.iter(|| day_15::day_15_v2(black_box(input_year_2016_day_15)))
+  });
+  g2016_day_15.finish();
+}
+
 criterion_group!(
   benches,
   year_2016_day_01,
@@ -197,6 +210,7 @@ criterion_group!(
   year_2016_day_11,
   year_2016_day_12,
   year_2016_day_13,
-  year_2016_day_14
+  year_2016_day_14,
+  year_2016_day_15
 );
 criterion_main!(benches);

inputs/year_2016/day_15_input

@@ -0,0 +1,6 @@
+Disc #1 has 13 positions; at time=0, it is at position 10.
+Disc #2 has 17 positions; at time=0, it is at position 15.
+Disc #3 has 19 positions; at time=0, it is at position 17.
+Disc #4 has 7 positions; at time=0, it is at position 1.
+Disc #5 has 5 positions; at time=0, it is at position 0.
+Disc #6 has 3 positions; at time=0, it is at position 1.

src/year_2016.rs

@@ -17,6 +17,7 @@ pub mod day_11;
 pub mod day_12;
 pub mod day_13;
 pub mod day_14;
+pub mod day_15;
 
 pub fn solve(day: u8, part: u8, input: impl Into<String>) -> Option<String> {
   if part != 1 && part != 2 {
@@ -38,6 +39,7 @@ pub fn solve(day: u8, part: u8, input: impl Into<String>) -> Option<String> {
     12 => Some(format!("{}", day_12::day_12(part, input))),
     13 => Some(format!("{}", day_13::day_13(part, input))),
     14 => Some(format!("{}", day_14::day_14(part, input))),
+    15 => Some(format!("{}", day_15::day_15(part, input))),
     _ => None,
   }
 }
@@ -152,4 +154,11 @@ mod tests {
     assert_eq!(day_14::day_14_v1(input), 25_427);
     assert_eq!(day_14::day_14_v2(input), 22_045);
   }
+
+  #[test]
+  fn day_15() {
+    let input = include_str!("../inputs/year_2016/day_15_input");
+    assert_eq!(day_15::day_15_v1(input), 203_660);
+    assert_eq!(day_15::day_15_v2(input), 2_408_135);
+  }
 }

src/year_2016/day_15.rs

@@ -0,0 +1,54 @@
+fn parse_disc(input: &str) -> (u32, u32, u32) {
+  let words: Vec<&str> = input.split_whitespace().collect();
+  let disc = words[1].strip_prefix('#').unwrap().parse::<u32>().unwrap();
+  let npos = words[3].parse::<u32>().unwrap();
+  let spos = words[11].strip_suffix('.').unwrap().parse::<u32>().unwrap();
+
+  (disc, npos, spos)
+}
+
+fn spin_the_discs(discs: Vec<(u32, u32, u32)>) -> u32 {
+  let mut period = 1;
+  let mut time = 0;
+  for (disc, npos, spos) in discs.iter() {
+    while ((time + disc + spos) % npos) != 0 {
+      time += period;
+    }
+    period *= npos;
+  }
+
+  time
+}
+
+pub fn day_15_v1(input: impl Into<String>) -> u32 {
+  let mut discs: Vec<(u32, u32, u32)> = vec![];
+  for line in input.into().lines() {
+    discs.push(parse_disc(line));
+  }
+
+  spin_the_discs(discs)
+}
+
+pub fn day_15_v2(input: impl Into<String>) -> u32 {
+  let mut discs: Vec<(u32, u32, u32)> = vec![];
+  for line in input.into().lines() {
+    discs.push(parse_disc(line));
+  }
+  discs.push(((discs.len() + 1) as u32, 11, 0));
+
+  spin_the_discs(discs)
+}
+
+solvable!(day_15, day_15_v1, day_15_v2, u32);
+
+#[cfg(test)]
+mod tests {
+  use super::*;
+
+  #[test]
+  fn works_with_samples_v1() {
+    let sample_one = "Disc #1 has 5 positions; at time=0, it is at position 4.\n\
+      Disc #2 has 2 positions; at time=0, it is at position 1.";
+    assert_eq!(day_15_v1(sample_one), 5);
+  }
+}