Day 13: Point of Incidence

README.md

@@ -17,4 +17,4 @@ Development occurs in language-specific directories:
 |[Day10.hs](hs/src/Day10.hs)|[Day10.kt](kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Day10.kt)|[day10.py](py/aoc2023/day10.py)|[day10.rs](rs/src/day10.rs)|
 |[Day11.hs](hs/src/Day11.hs)|[Day11.kt](kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Day11.kt)|[day11.py](py/aoc2023/day11.py)|[day11.rs](rs/src/day11.rs)|
 |[Day12.hs](hs/src/Day12.hs)|[Day12.kt](kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Day12.kt)|[day12.py](py/aoc2023/day12.py)|[day12.rs](rs/src/day12.rs)|
-|[Day13.hs](hs/src/Day13.hs)|[Day13.kt](kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Day13.kt)|[day13.py](py/aoc2023/day13.py)||
+|[Day13.hs](hs/src/Day13.hs)|[Day13.kt](kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Day13.kt)|[day13.py](py/aoc2023/day13.py)|[day13.rs](rs/src/day13.rs)|

rs/benches/criterion.rs

@@ -1,4 +1,4 @@
-use aoc2023::{day1, day10, day11, day12, day2, day3, day4, day5, day6, day7, day8, day9};
+use aoc2023::{day1, day10, day11, day12, day13, day2, day3, day4, day5, day6, day7, day8, day9};
 use criterion::{black_box, Criterion};
 use std::env;
 use std::fs;
@@ -86,6 +86,12 @@ fn aoc2023_bench(c: &mut Criterion) -> io::Result<()> {
     g.bench_function("part 2", |b| b.iter(|| day12::part2(black_box(&data))));
     g.finish();
 
+    let data = get_day_input(13)?;
+    let mut g = c.benchmark_group("day 13");
+    g.bench_function("part 1", |b| b.iter(|| day13::part1(black_box(&data))));
+    g.bench_function("part 2", |b| b.iter(|| day13::part2(black_box(&data))));
+    g.finish();
+
     Ok(())
 }
 

rs/src/day13.rs

@@ -0,0 +1,84 @@
+fn find_reflection<T: Eq, F: Fn(&[T], &[T]) -> bool>(data: &[T], eq: F) -> usize {
+    (1..data.len())
+        .find(|&i| eq(&data[..i], &data[i..]))
+        .unwrap_or_default()
+}
+
+fn solve<F: Fn(&[&str], &[&str]) -> bool>(lines: &[&str], eq: F) -> usize {
+    let width = lines
+        .iter()
+        .map(|line| line.len())
+        .max()
+        .unwrap_or_default();
+    let transpose = (0..width)
+        .map(|i| {
+            lines
+                .iter()
+                .flat_map(|line| line[i..i + 1].chars())
+                .collect::<String>()
+        })
+        .collect::<Vec<_>>();
+    let transpose = transpose.iter().map(|line| &line[..]).collect::<Vec<_>>();
+
+    100 * find_reflection(lines, &eq) + find_reflection(&transpose, &eq)
+}
+
+pub fn part1(data: &str) -> usize {
+    data.split("\n\n")
+        .map(|group| {
+            solve(&group.lines().collect::<Vec<_>>(), |x, y| {
+                x.iter().rev().zip(y.iter()).all(|(a, b)| a == b)
+            })
+        })
+        .sum()
+}
+
+pub fn part2(data: &str) -> usize {
+    data.split("\n\n")
+        .map(|group| {
+            solve(&group.lines().collect::<Vec<_>>(), |x, y| {
+                let mut iter = x
+                    .iter()
+                    .rev()
+                    .zip(y.iter())
+                    .flat_map(|(a, b)| a.chars().zip(b.chars()).filter(|(c, d)| c != d));
+                iter.next().is_some() && iter.next().is_none()
+            })
+        })
+        .sum()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use indoc::indoc;
+    use pretty_assertions::assert_eq;
+
+    static EXAMPLE: &str = indoc! {"
+        #.##..##.
+        ..#.##.#.
+        ##......#
+        ##......#
+        ..#.##.#.
+        ..##..##.
+        #.#.##.#.
+
+        #...##..#
+        #....#..#
+        ..##..###
+        #####.##.
+        #####.##.
+        ..##..###
+        #....#..#
+    "};
+
+    #[test]
+    fn part1_examples() {
+        assert_eq!(405, part1(EXAMPLE));
+    }
+
+    #[test]
+    fn part2_examples() {
+        assert_eq!(400, part2(EXAMPLE));
+    }
+}

rs/src/lib.rs

@@ -2,6 +2,7 @@ pub mod day1;
 pub mod day10;
 pub mod day11;
 pub mod day12;
+pub mod day13;
 pub mod day2;
 pub mod day3;
 pub mod day4;

rs/src/main.rs

@@ -1,4 +1,4 @@
-use aoc2023::{day1, day10, day11, day12, day2, day3, day4, day5, day6, day7, day8, day9};
+use aoc2023::{day1, day10, day11, day12, day13, day2, day3, day4, day5, day6, day7, day8, day9};
 use std::collections::HashSet;
 use std::env;
 use std::fs;
@@ -112,5 +112,13 @@ fn main() -> io::Result<()> {
         println!();
     }
 
+    if args.is_empty() || args.contains("13") {
+        println!("Day 13");
+        let data = get_day_input(13)?;
+        println!("{:?}", day13::part1(&data));
+        println!("{:?}", day13::part2(&data));
+        println!();
+    }
+
     Ok(())
 }