Day 24: Blizzard Basin

rs/benches/criterion.rs

@@ -3,7 +3,7 @@ extern crate build_const;
 
 use aoc2022::{
     day1, day10, day11, day12, day13, day13_fast, day14, day15, day16, day17, day18, day19, day2,
-    day20, day21, day22, day23, day3, day4, day5, day6, day7, day8, day9,
+    day20, day21, day22, day23, day24, day3, day4, day5, day6, day7, day8, day9,
 };
 use criterion::{black_box, criterion_group, criterion_main, Criterion};
 use gag::Gag;
@@ -115,6 +115,10 @@ fn aoc2022_bench(c: &mut Criterion) {
     g.bench_function("part 1", |b| b.iter(|| day23::part1(black_box(DAY23))));
     g.bench_function("part 2", |b| b.iter(|| day23::part2(black_box(DAY23))));
     g.finish();
+    let mut g = c.benchmark_group("day 24");
+    g.bench_function("part 1", |b| b.iter(|| day24::part1(black_box(DAY24))));
+    g.bench_function("part 2", |b| b.iter(|| day24::part2(black_box(DAY24))));
+    g.finish();
 }
 
 criterion_group!(aoc2022, aoc2022_bench);

rs/src/day24.rs

@@ -0,0 +1,111 @@
+use std::cmp::Reverse;
+use std::collections::{BinaryHeap, HashSet};
+use std::ops::Range;
+
+fn add_mod_range(a: usize, b: usize, range: Range<usize>) -> usize {
+    (a - range.start + b) % range.len() + range.start
+}
+
+fn sub_mod_range(a: usize, b: usize, range: Range<usize>) -> usize {
+    (a - range.start + range.len() - b % range.len()) % range.len() + range.start
+}
+
+fn search(
+    lines: &[&[u8]],
+    start: (usize, usize),
+    end: (usize, usize),
+    time: usize,
+) -> Option<usize> {
+    let mut seen: HashSet<_> = [(start, time)].into();
+    let mut queue: BinaryHeap<_> = [(Reverse(0), (start, time))].into();
+    while let Some((_, (pos @ (x, y), time))) = queue.pop() {
+        if pos == end {
+            return Some(time);
+        }
+        for (dx, dy) in [(-1, 0), (0, -1), (0, 0), (0, 1), (1, 0)] {
+            let Some(x) = x.checked_add_signed(dx) else { continue };
+            let Some(y) = y.checked_add_signed(dy) else { continue };
+            if y >= lines.len() || x == 0 {
+                continue;
+            }
+            let line = lines[y];
+            if x >= line.len() - 1 {
+                continue;
+            }
+            if y == 0 || y == lines.len() - 1 {
+                if lines[y][x] != b'.' {
+                    continue;
+                }
+            } else if line[add_mod_range(x, time + 1, 1..line.len() - 1)] == b'<'
+                || line[sub_mod_range(x, time + 1, 1..line.len() - 1)] == b'>'
+                || lines[add_mod_range(y, time + 1, 1..lines.len() - 1)][x] == b'^'
+                || lines[sub_mod_range(y, time + 1, 1..lines.len() - 1)][x] == b'v'
+            {
+                continue;
+            }
+            if seen.insert(((x, y), time + 1)) {
+                queue.push((
+                    Reverse(time + x.abs_diff(end.0) + y.abs_diff(end.1)),
+                    ((x, y), time + 1),
+                ));
+            }
+        }
+    }
+    None
+}
+
+pub fn part1<'a, I, S>(lines: I) -> Option<usize>
+where
+    I: IntoIterator<Item = &'a S>,
+    S: AsRef<str> + 'a,
+{
+    let lines = lines
+        .into_iter()
+        .map(|line| line.as_ref().as_bytes())
+        .collect::<Vec<_>>();
+    search(
+        &lines,
+        (1, 0),
+        (lines.last()?.len() - 2, lines.len() - 1),
+        0,
+    )
+}
+
+pub fn part2<'a, I, S>(lines: I) -> Option<usize>
+where
+    I: IntoIterator<Item = &'a S>,
+    S: AsRef<str> + 'a,
+{
+    let lines = lines
+        .into_iter()
+        .map(|line| line.as_ref().as_bytes())
+        .collect::<Vec<_>>();
+    let start = (1, 0);
+    let end = (lines.last()?.len() - 2, lines.len() - 1);
+    search(
+        &lines,
+        start,
+        end,
+        search(&lines, end, start, search(&lines, start, end, 0)?)?,
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use pretty_assertions::assert_eq;
+
+    static EXAMPLE: &[&str] = &[
+        "#.######", "#>>.<^<#", "#.<..<<#", "#>v.><>#", "#<^v^^>#", "######.#",
+    ];
+
+    #[test]
+    fn part1_examples() {
+        assert_eq!(Some(18), part1(EXAMPLE));
+    }
+
+    #[test]
+    fn part2_examples() {
+        assert_eq!(Some(54), part2(EXAMPLE));
+    }
+}

rs/src/lib.rs

@@ -15,6 +15,7 @@ pub mod day20;
 pub mod day21;
 pub mod day22;
 pub mod day23;
+pub mod day24;
 pub mod day3;
 pub mod day4;
 pub mod day5;

rs/src/main.rs

@@ -3,7 +3,7 @@ extern crate build_const;
 
 use aoc2022::{
     day1, day10, day11, day12, day13, day13_fast, day14, day15, day16, day17, day18, day19, day2,
-    day20, day21, day22, day23, day3, day4, day5, day6, day7, day8, day9,
+    day20, day21, day22, day23, day24, day3, day4, day5, day6, day7, day8, day9,
 };
 use std::collections::HashSet;
 use std::env;
@@ -184,5 +184,12 @@ fn main() -> io::Result<()> {
         println!();
     }
 
+    if args.is_empty() || args.contains("24") {
+        println!("Day 24");
+        println!("{:?}", day24::part1(DAY24).expect("error"));
+        println!("{:?}", day24::part2(DAY24).expect("error"));
+        println!();
+    }
+
     Ok(())
 }