Year 2017: Day 17

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)
 
+## [2017.17.1]
+### Added
+- Solved [exercice for 2017, day 17](src/year_2017/17.rs).
+
 ## [2017.16.1]
 ### Added
 - Solved [exercice for 2017, day 16](src/year_2017/16.rs).

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "advent-rs"
-version = "2017.16.1"
+version = "2017.17.1"
 edition = "2021"
 authors = ["Arnaud 'red' Rouyer"]
 readme = "README.md"

NOTES_2017.md

@@ -67,3 +67,7 @@ The most interesting part of these exercises is often [all the obscure maths you
 ## Day 16: Permutation Promenade
 
 Nothing hard, until you see how much ONE BILLION ITERATIONS actually is. Good news though: "All loops are about knowing when to stop". In that case, we can just...look for a repetition of the pattern.
+
+## Day 17: Spinlock
+
+As always, there's a trick to avoid looping too much: since `0` is ALWAYS at the 0th position, we just have to store the last number we are inserting  (allegedly, no need to allocate a real Vec) after it.

README.md

@@ -7,7 +7,7 @@ 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, complete!](NOTES_2016.md)
-- [2017, up to day 16](NOTES_2017.md)
+- [2017, up to day 17](NOTES_2017.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_2017.rs

@@ -14,6 +14,7 @@ use advent_rs::year_2017::day_13;
 use advent_rs::year_2017::day_14;
 use advent_rs::year_2017::day_15;
 use advent_rs::year_2017::day_16;
+use advent_rs::year_2017::day_17;
 use criterion::{black_box, criterion_group, criterion_main, Criterion};
 
 fn year_2017_day_01(c: &mut Criterion) {
@@ -259,6 +260,21 @@ fn year_2017_day_16(c: &mut Criterion) {
   g2017_day_16.finish();
 }
 
+fn year_2017_day_17(c: &mut Criterion) {
+  let input_day_17 = include_str!("../inputs/year_2017/day_17_input");
+  assert_eq!(day_17::day_17_v1(input_day_17), 1_173);
+  assert_eq!(day_17::day_17_v2(input_day_17), 1_930_815);
+
+  let mut g2017_day_17 = c.benchmark_group("year_2017::day_17");
+  g2017_day_17.bench_function("year_2017::day_17_v1", |b| {
+    b.iter(|| day_17::day_17_v1(black_box(input_day_17)))
+  });
+  g2017_day_17.bench_function("year_2017::day_17_v2", |b| {
+    b.iter(|| day_17::day_17_v2(black_box(input_day_17)))
+  });
+  g2017_day_17.finish();
+}
+
 criterion_group!(
   benches,
   year_2017_day_01,
@@ -276,6 +292,7 @@ criterion_group!(
   year_2017_day_13,
   year_2017_day_14,
   year_2017_day_15,
-  year_2017_day_16
+  year_2017_day_16,
+  year_2017_day_17
 );
 criterion_main!(benches);

inputs/year_2017/day_17_input

@@ -0,0 +1 @@
+304

src/year_2017.rs

@@ -20,6 +20,7 @@ pub mod day_13;
 pub mod day_14;
 pub mod day_15;
 pub mod day_16;
+pub mod day_17;
 
 pub fn solve(day: u8, part: u8, input: impl Into<String>) -> Option<String> {
   if part > 2 {
@@ -43,6 +44,7 @@ pub fn solve(day: u8, part: u8, input: impl Into<String>) -> Option<String> {
     14 => Some(day_14::day_14(part, input).to_string()),
     15 => Some(day_15::day_15(part, input).to_string()),
     16 => Some(day_16::day_16(part, input).to_string()),
+    17 => Some(day_17::day_17(part, input).to_string()),
     _ => None,
   }
 }
@@ -162,4 +164,11 @@ mod tests {
     assert_eq!(day_16::day_16_v1(input), "lgpkniodmjacfbeh");
     assert_eq!(day_16::day_16_v2(input), "hklecbpnjigoafmd");
   }
+
+  #[test]
+  fn day_17() {
+    let input = include_str!("../inputs/year_2017/day_17_input");
+    assert_eq!(day_17::day_17_v1(input), 1_173);
+    assert_eq!(day_17::day_17_v2(input), 1_930_815);
+  }
 }

src/year_2017/day_17.rs

@@ -0,0 +1,38 @@
+pub fn day_17_v1(input: impl Into<String>) -> u32 {
+  let input = input.into().trim_end().parse::<u32>().unwrap();
+  let mut spinlock: Vec<u32> = vec![0];
+  let mut idx = 0;
+  for i in 1..=2017 {
+    idx = ((idx + input) % spinlock.len() as u32) + 1;
+    spinlock.insert(idx as usize, i);
+  }
+
+  idx = spinlock.iter().position(|n| *n == 2017).unwrap() as u32;
+  idx = (idx + 1) % spinlock.len() as u32;
+  spinlock[idx as usize]
+}
+
+pub fn day_17_v2(input: impl Into<String>) -> u32 {
+  let input = input.into().trim_end().parse::<u32>().unwrap();
+  let mut answer = 0;
+  let mut idx = 0;
+  for i in 1..=5_000_000 {
+    idx = (idx + input) % i;
+    if idx == 0 {
+      answer = i;
+    }
+    idx += 1;
+  }
+  answer
+}
+solvable!(day_17, day_17_v1, day_17_v2, u32);
+
+#[cfg(test)]
+mod tests {
+  use super::*;
+
+  #[test]
+  fn works_with_samples_v1() {
+    assert_eq!(day_17_v1("3"), 638);
+  }
+}