Day 23: A Long Walk (part 1)

README.md

@@ -27,5 +27,5 @@ Development occurs in language-specific directories:
 |[Day20.hs](hs/src/Day20.hs)|[Day20.kt](kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Day20.kt)|[day20.py](py/aoc2023/day20.py)|[day20.rs](rs/src/day20.rs)|
 |[Day21.hs](hs/src/Day21.hs)|[Day21.kt](kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Day21.kt)|[day21.py](py/aoc2023/day21.py)|[day21.rs](rs/src/day21.rs)|
 |[Day22.hs](hs/src/Day22.hs)|[Day22.kt](kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Day22.kt)|[day22.py](py/aoc2023/day22.py)|[day22.rs](rs/src/day22.rs)|
-||[Day23.kt](kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Day23.kt)|||
+||[Day23.kt](kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Day23.kt)||[day23.rs](rs/src/day23.rs) ½|
 |[Day24.hs](hs/src/Day24.hs) ½|[Day24.kt](kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Day24.kt) ½|[day24.py](py/aoc2023/day24.py) ½|[day24.rs](rs/src/day24.rs) ½|

rs/benches/criterion.rs

@@ -1,6 +1,6 @@
 use aoc2023::{
     day1, day10, day11, day12, day13, day14, day15, day16, day17, day18, day19, day2, day20, day21,
-    day22, day24, day3, day4, day5, day6, day7, day8, day9,
+    day22, day23, day24, day3, day4, day5, day6, day7, day8, day9,
 };
 use criterion::{black_box, Criterion};
 use std::env;
@@ -149,6 +149,11 @@ fn aoc2023_bench(c: &mut Criterion) -> io::Result<()> {
     g.bench_function("part 2", |b| b.iter(|| day22::part2(black_box(&data))));
     g.finish();
 
+    let data = get_day_input(23)?;
+    let mut g = c.benchmark_group("day 23");
+    g.bench_function("part 1", |b| b.iter(|| day23::part1(black_box(&data))));
+    g.finish();
+
     let data = get_day_input(24)?;
     let mut g = c.benchmark_group("day 24");
     g.bench_function("part 1", |b| b.iter(|| day24::part1(black_box(&data))));

rs/src/day23.rs

@@ -0,0 +1,106 @@
+use std::collections::{BTreeMap, BTreeSet};
+
+pub fn part1(data: &str) -> Option<usize> {
+    let grid = data.lines().map(|line| line.as_bytes()).collect::<Vec<_>>();
+    let graph = grid
+        .iter()
+        .enumerate()
+        .flat_map(|(y, row)| {
+            let grid = &grid;
+            row.iter().enumerate().filter_map(move |(x, c)| {
+                if [b'.', b'<', b'>', b'^', b'v'].contains(c) {
+                    let mut edges = BTreeMap::new();
+                    if b".<".contains(c) && x > 0 && b".<".contains(&row[x - 1]) {
+                        edges.insert((y, x - 1), 1);
+                    }
+                    if b".>".contains(c) && x + 1 < row.len() && b".>".contains(&row[x + 1]) {
+                        edges.insert((y, x + 1), 1);
+                    }
+                    if b".^".contains(c) && y > 0 {
+                        let row = grid[y - 1];
+                        if x < row.len() && b".^".contains(&row[x]) {
+                            edges.insert((y - 1, x), 1);
+                        }
+                    }
+                    if b".v".contains(c) && y + 1 < grid.len() {
+                        let row = grid[y + 1];
+                        if x < row.len() && b".v".contains(&row[x]) {
+                            edges.insert((y + 1, x), 1);
+                        }
+                    }
+                    Some(((y, x), edges))
+                } else {
+                    None
+                }
+            })
+        })
+        .collect::<BTreeMap<_, _>>();
+    let start = *graph.keys().next()?;
+    let end = *graph.keys().next_back()?;
+
+    let mut stack = vec![(start, BTreeSet::from([start]), 0)];
+    let mut best = None::<usize>;
+    while let Some((node, used, distance)) = stack.pop() {
+        if node == end {
+            best = Some(best.map_or(distance, |best| best.max(distance)));
+        }
+        let Some(edges) = graph.get(&node) else {
+            continue;
+        };
+        for (next, weight) in edges {
+            let mut used = used.clone();
+            if used.insert(*next) {
+                stack.push((*next, used, distance + weight));
+            }
+        }
+    }
+
+    best
+}
+
+pub fn part2(data: &str) -> Option<usize> {
+    part1(&data.replace(|c| "<>^v".contains(c), "."))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use indoc::indoc;
+    use pretty_assertions::assert_eq;
+
+    static EXAMPLE: &str = indoc! {"
+        #.#####################
+        #.......#########...###
+        #######.#########.#.###
+        ###.....#.>.>.###.#.###
+        ###v#####.#v#.###.#.###
+        ###.>...#.#.#.....#...#
+        ###v###.#.#.#########.#
+        ###...#.#.#.......#...#
+        #####.#.#.#######.#.###
+        #.....#.#.#.......#...#
+        #.#####.#.#.#########v#
+        #.#...#...#...###...>.#
+        #.#.#v#######v###.###v#
+        #...#.>.#...>.>.#.###.#
+        #####v#.#.###v#.#.###.#
+        #.....#...#...#.#.#...#
+        #.#########.###.#.#.###
+        #...###...#...#...#.###
+        ###.###.#.###v#####v###
+        #...#...#.#.>.>.#.>.###
+        #.###.###.#.###.#.#v###
+        #.....###...###...#...#
+        #####################.#
+    "};
+
+    #[test]
+    fn part1_examples() {
+        assert_eq!(Some(94), part1(EXAMPLE));
+    }
+
+    #[test]
+    fn part2_examples() {
+        assert_eq!(Some(154), part2(EXAMPLE));
+    }
+}

rs/src/lib.rs

@@ -13,6 +13,7 @@ pub mod day2;
 pub mod day20;
 pub mod day21;
 pub mod day22;
+pub mod day23;
 pub mod day24;
 pub mod day3;
 pub mod day4;

rs/src/main.rs

@@ -1,6 +1,6 @@
 use aoc2023::{
     day1, day10, day11, day12, day13, day14, day15, day16, day17, day18, day19, day2, day20, day21,
-    day22, day24, day3, day4, day5, day6, day7, day8, day9,
+    day22, day23, day24, day3, day4, day5, day6, day7, day8, day9,
 };
 use std::collections::HashSet;
 use std::env;
@@ -195,6 +195,13 @@ fn main() -> io::Result<()> {
         println!();
     }
 
+    if args.is_empty() || args.contains("23") {
+        println!("Day 23");
+        let data = get_day_input(23)?;
+        println!("{:?}", day23::part1(&data).expect("error"));
+        println!();
+    }
+
     if args.is_empty() || args.contains("24") {
         println!("Day 24");
         let data = get_day_input(24)?;