2018 day 1

Author: ictrobot

Cargo.lock

@@ -13,6 +13,7 @@ utils = { path = "../utils", default-features = false }
 year2015 = { path = "../year2015", optional = true }
 year2016 = { path = "../year2016", optional = true }
 year2017 = { path = "../year2017", optional = true }
+year2018 = { path = "../year2018", optional = true }
 year2024 = { path = "../year2024", optional = true }
 
 [features]
@@ -21,8 +22,8 @@ const_lut = ["year2024?/const_lut"]
 all-simd = ["utils/all-simd"]
 test-runner = []
 # xtask update features
-all-years = ["year2015", "year2016", "year2017", "year2024"]
-unsafe = ["year2015?/unsafe", "year2016?/unsafe", "year2017?/unsafe", "year2024?/unsafe", "utils/unsafe"]
+all-years = ["year2015", "year2016", "year2017", "year2018", "year2024"]
+unsafe = ["year2015?/unsafe", "year2016?/unsafe", "year2017?/unsafe", "year2018?/unsafe", "year2024?/unsafe", "utils/unsafe"]
 
 [lints]
 workspace = true

crates/aoc/Cargo.toml

@@ -23,6 +23,10 @@ pub mod year2016 {
 pub mod year2017 {
     pub use ::utils::puzzles_noop as puzzles;
 }
+#[cfg(not(feature = "year2018"))]
+pub mod year2018 {
+    pub use ::utils::puzzles_noop as puzzles;
+}
 #[cfg(not(feature = "year2024"))]
 pub mod year2024 {
     pub use ::utils::puzzles_noop as puzzles;
@@ -33,6 +37,8 @@ pub use ::year2015;
 pub use ::year2016;
 #[cfg(feature = "year2017")]
 pub use ::year2017;
+#[cfg(feature = "year2018")]
+pub use ::year2018;
 #[cfg(feature = "year2024")]
 pub use ::year2024;
 
@@ -104,6 +110,7 @@ macro_rules! all_puzzles {
                 $crate::year2015::puzzles,
                 $crate::year2016::puzzles,
                 $crate::year2017::puzzles,
+                $crate::year2018::puzzles,
                 $crate::year2024::puzzles,
 
                 $callback

crates/aoc/src/years.rs

@@ -0,0 +1,14 @@
+[package]
+name = "year2018"
+authors = { workspace = true }
+edition = { workspace = true }
+license = { workspace = true }
+publish = { workspace = true }
+repository = { workspace = true }
+rust-version = { workspace = true }
+
+[dependencies]
+utils = { path = "../utils", default-features = false }
+
+[features]
+unsafe = ["utils/unsafe"]

crates/year2018/Cargo.toml

@@ -0,0 +1 @@
+Solutions for [Advent of Code 2018](https://adventofcode.com/2018)

crates/year2018/README.md

@@ -0,0 +1,111 @@
+use std::iter;
+use utils::prelude::*;
+
+/// Finding the first repeat.
+#[derive(Clone, Debug)]
+pub struct Day01 {
+    changes: Vec<i32>,
+    total: i32,
+}
+
+impl Day01 {
+    pub fn new(input: &str, _: InputType) -> Result<Self, InputError> {
+        let changes = parser::i32().parse_lines(input)?;
+        Ok(Self {
+            total: changes.iter().sum(),
+            changes,
+        })
+    }
+
+    #[must_use]
+    pub fn part1(&self) -> i32 {
+        self.total
+    }
+
+    #[must_use]
+    pub fn part2(&self) -> i32 {
+        if self.total == 0 {
+            let mut frequencies = iter::once(0)
+                .chain(self.changes.iter().scan(0i32, |sum, &c| {
+                    *sum += c;
+                    Some(*sum)
+                }))
+                .enumerate()
+                .collect::<Vec<_>>();
+
+            frequencies.sort_unstable_by_key(|&(idx, freq)| (freq, idx));
+
+            frequencies
+                .windows(2)
+                .filter_map(|w| {
+                    let (_, freq1) = w[0];
+                    let (idx2, freq2) = w[1];
+                    if freq1 == freq2 {
+                        Some((idx2, freq1))
+                    } else {
+                        None
+                    }
+                })
+                .min()
+        } else {
+            let mut remainders = self
+                .changes
+                .iter()
+                .enumerate()
+                .scan(0i32, |freq, (t, &change)| {
+                    let curr = *freq;
+                    *freq += change;
+                    Some((curr.rem_euclid(self.total), curr, t))
+                })
+                .collect::<Vec<_>>();
+
+            remainders.sort_unstable();
+
+            remainders
+                .chunk_by(|&(r1, _, _), &(r2, _, _)| r1 == r2)
+                .flat_map(|chunk| {
+                    chunk.iter().enumerate().flat_map(|(i, &r1)| {
+                        chunk.iter().skip(i + 1).filter_map(move |&r2| {
+                            let ((_, freq1, t1), (_, freq2, _)) =
+                                if self.total > 0 { (r1, r2) } else { (r2, r1) };
+
+                            let freq_difference = freq2 - freq1;
+                            let iterations = freq_difference / self.total;
+                            if freq_difference.rem_euclid(self.total) == 0 && iterations >= 0 {
+                                let iterations = iterations as usize;
+                                Some((iterations * self.changes.len() + t1, freq2))
+                            } else {
+                                None
+                            }
+                        })
+                    })
+                })
+                .min()
+        }
+        .map(|(_, freq)| freq)
+        .expect("no solution found")
+    }
+}
+
+examples!(Day01 -> (i32, i32) [
+    {input: "+1\n-2\n+3\n+1", part1: 3, part2: 2},
+    {input: "+1\n+1\n+1", part1: 3},
+    {input: "+1\n+1\n-2", part1: 0},
+    {input: "-1\n-2\n-3", part1: -6},
+    {input: "+1\n-1", part2: 0},
+    {input: "+3\n+3\n+4\n-2\n-4", part2: 10},
+    {input: "-6\n+3\n+8\n+5\n-6", part2: 5},
+    {input: "+7\n+7\n-2\n-7\n-4", part2: 14},
+    // Negative versions of the above
+    {input: "-1\n+2\n-3\n-1", part1: -3, part2: -2},
+    {input: "-1\n+1", part2: 0},
+    {input: "-3\n-3\n-4\n+2\n+4", part2: -10},
+    {input: "+6\n-3\n-8\n-5\n+6", part2: -5},
+    {input: "-7\n-7\n+2\n+7\n+4", part2: -14},
+    // Custom examples
+    {input: "+2\n+3\n-8", part2: 2},
+    {input: "+0", part2: 0},
+    {input: "+1000000\n-999999", part2: 1000000},
+    {input: "+1\n-2\n+2\n-2\n+3", part2: 1},
+    {input: "+1\n-2\n+2\n-2\n-5", part2: 1},
+]);

crates/year2018/src/day01.rs

@@ -0,0 +1,6 @@
+#![doc = include_str!("../README.md")]
+#![cfg_attr(not(feature = "unsafe"), forbid(unsafe_code))]
+
+utils::year!(2018 => year2018, ${
+    1 => day01::Day01,
+});