2023 day 10.

nerdatmath · nerdatmath · commit c205f8afe716 · 2025-09-29T21:42:05.000-05:00
diff --git a/2023/10/.gitignore b/2023/10/.gitignore
@@ -0,0 +1 @@
+/target
diff --git a/2023/10/Cargo.toml b/2023/10/Cargo.toml
@@ -0,0 +1,10 @@
+[package]
+name = "y2023d10"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+anyhow = "1.0.99"
+game-grid.workspace = true
+thiserror = "2.0.15"
+direction.workspace = true
diff --git a/2023/10/data/example1 b/2023/10/data/example1
@@ -0,0 +1,5 @@
+.....
+.S-7.
+.|.|.
+.L-J.
+.....
diff --git a/2023/10/data/example2 b/2023/10/data/example2
@@ -0,0 +1,5 @@
+..F7.
+.FJ|.
+SJ.L7
+|F--J
+LJ...
diff --git a/2023/10/data/example3 b/2023/10/data/example3
@@ -0,0 +1,9 @@
+...........
+.S-------7.
+.|F-----7|.
+.||.....||.
+.||.....||.
+.|L-7.F-J|.
+.|..|.|..|.
+.L--J.L--J.
+...........
diff --git a/2023/10/data/example4 b/2023/10/data/example4
@@ -0,0 +1,10 @@
+.F----7F7F7F7F-7....
+.|F--7||||||||FJ....
+.||.FJ||||||||L7....
+FJL7L7LJLJ||LJ.L-7..
+L--J.L7...LJS7F-7L7.
+....F-J..F7FJ|L7L7L7
+....L7.F7||L7|.L7L7|
+.....|FJLJ|FJ|F7|.LJ
+....FJL-7.||.||||...
+....L---J.LJ.LJLJ...
diff --git a/2023/10/data/example5 b/2023/10/data/example5
@@ -0,0 +1,10 @@
+FF7FSF7F7F7F7F7F---7
+L|LJ||||||||||||F--J
+FL-7LJLJ||||||LJL-77
+F--JF--7||LJLJ7F7FJ-
+L---JF-JLJ.||-FJLJJ7
+|F|F-JF---7F7-L7L|7|
+|FFJF7L7F-JF7|JL---7
+7-L-JL7||F7|L7F-7F7|
+L.L7LFJ|||||FJL7||LJ
+L7JLJL-JLJLJL--JLJ.L
diff --git a/2023/10/data/input b/2023/10/data/input
diff --git a/2023/10/src/data.rs b/2023/10/src/data.rs
@@ -0,0 +1,17 @@
+#[cfg(test)]
+pub const EXAMPLE1: &'static str = include_str!("../data/example1");
+
+#[cfg(test)]
+pub const EXAMPLE2: &'static str = include_str!("../data/example2");
+
+#[cfg(test)]
+pub const EXAMPLE3: &'static str = include_str!("../data/example3");
+
+#[cfg(test)]
+pub const EXAMPLE4: &'static str = include_str!("../data/example4");
+
+#[cfg(test)]
+pub const EXAMPLE5: &'static str = include_str!("../data/example5");
+
+#[allow(unused)]
+pub const INPUT: &'static str = include_str!("../data/input");
diff --git a/2023/10/src/main.rs b/2023/10/src/main.rs
@@ -0,0 +1,12 @@
+mod data;
+mod part1;
+mod part2;
+mod pipe;
+mod position;
+mod puzzle;
+
+fn main() {
+    use data::INPUT;
+    println!("Part 1: {}", part1::run(INPUT));
+    println!("Part 2: {}", part2::run(INPUT));
+}
diff --git a/2023/10/src/part1/mod.rs b/2023/10/src/part1/mod.rs
@@ -0,0 +1,23 @@
+use crate::*;
+use puzzle::Puzzle;
+
+pub fn run(input: &str) -> usize {
+    let puzzle: Puzzle = input.parse().expect("parse failed");
+    puzzle.iter().count() / 2
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use crate::data;
+
+    #[test]
+    fn test1() {
+        assert_eq!(run(data::EXAMPLE1), 4);
+    }
+
+    #[test]
+    fn test2() {
+        assert_eq!(run(data::EXAMPLE2), 8);
+    }
+}
diff --git a/2023/10/src/part2/mod.rs b/2023/10/src/part2/mod.rs
@@ -0,0 +1,96 @@
+use direction::Direction;
+
+use crate::position::Position;
+use crate::puzzle::Puzzle;
+
+fn shoelace(mut iter: impl Iterator<Item = Position>) -> i32 {
+    let start = iter.next().expect("shoelace: iter must not be empty");
+    let mut prev = start;
+    let mut area = 0i32;
+    for pos in iter {
+        area += prev.x * pos.y - pos.x * prev.y;
+        prev = pos;
+    }
+    area += prev.x * start.y - start.x * prev.y;
+    area / 2
+}
+
+fn left_offset(r#in: Direction, out: Direction) -> (i32, i32) {
+    use Direction::*;
+    match (r#in, out) {
+        (N, E) | (E, N) => (-1, -1),
+        (N, W) | (W, N) => (-1, 1),
+        (S, E) | (E, S) => (1, -1),
+        (S, W) | (W, S) => (1, 1),
+        (N, N) => (-1, 0),
+        (S, S) => (1, 0),
+        (E, E) => (0, -1),
+        (W, W) => (0, 1),
+        _ => unreachable!(),
+    }
+}
+
+fn left_area(puzzle: &Puzzle) -> i32 {
+    shoelace(puzzle.iter().map(|state| {
+        state.position * 2
+            + (1, 1)
+            + left_offset(
+                state
+                    .pipe
+                    .next_direction(state.direction.reverse())
+                    .expect("bad pipe / direction combo")
+                    .reverse(),
+                state.direction,
+            )
+    })) / 4
+}
+
+fn right_area(puzzle: &Puzzle) -> i32 {
+    shoelace(puzzle.iter().map(|state| {
+        state.position * 2 + (1, 1)
+            - left_offset(
+                state
+                    .pipe
+                    .next_direction(state.direction.reverse())
+                    .expect("bad pipe / direction combo")
+                    .reverse(),
+                state.direction,
+            )
+    })) / 4
+}
+
+pub fn run(input: &str) -> usize {
+    let puzzle: Puzzle = input.parse().expect("parse failed");
+    left_area(&puzzle)
+        .abs()
+        .min(right_area(&puzzle).abs())
+        .try_into()
+        .expect("abs() returned a negative number")
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use crate::data;
+
+    #[test]
+    fn test1() {
+        assert_eq!(run(data::EXAMPLE1), 1);
+    }
+    #[test]
+    fn test2() {
+        assert_eq!(run(data::EXAMPLE2), 1);
+    }
+    #[test]
+    fn test3() {
+        assert_eq!(run(data::EXAMPLE3), 4);
+    }
+    #[test]
+    fn test4() {
+        assert_eq!(run(data::EXAMPLE4), 8);
+    }
+    #[test]
+    fn test5() {
+        assert_eq!(run(data::EXAMPLE5), 10);
+    }
+}
diff --git a/2023/10/src/pipe.rs b/2023/10/src/pipe.rs
@@ -0,0 +1,50 @@
+use direction::Direction;
+use game_grid::GridCell;
+use game_grid::ParseCellError;
+
+#[derive(GridCell, Copy, Clone, Debug, PartialEq, Eq, Default)]
+pub enum Pipe {
+    #[cell('.')]
+    #[default]
+    Ground,
+    #[cell('|')]
+    NorthSouth,
+    #[cell('-')]
+    EastWest,
+    #[cell('L')]
+    NorthEast,
+    #[cell('J')]
+    NorthWest,
+    #[cell('7')]
+    SouthWest,
+    #[cell('F')]
+    SouthEast,
+    #[cell('S')]
+    Start,
+}
+
+impl Pipe {
+    pub fn next_direction(&self, direction: Direction) -> Option<Direction> {
+        use Direction::*;
+        use Pipe::*;
+        Some(match (*self, direction) {
+            (NorthSouth, N) => N,
+            (NorthSouth, S) => S,
+            (EastWest, E) => E,
+            (EastWest, W) => W,
+            (NorthEast, S) => E,
+            (NorthEast, W) => N,
+            (NorthWest, S) => W,
+            (NorthWest, E) => N,
+            (SouthWest, N) => W,
+            (SouthWest, E) => S,
+            (SouthEast, N) => E,
+            (SouthEast, W) => S,
+            _ => return None,
+        })
+    }
+
+    pub fn has_direction(&self, direction: Direction) -> bool {
+        self.next_direction(direction).is_some()
+    }
+}
diff --git a/2023/10/src/position.rs b/2023/10/src/position.rs
@@ -0,0 +1,55 @@
+use std::ops::{Add, Mul, Sub};
+
+use direction::Direction;
+use game_grid::GridPosition;
+
+#[derive(Debug, Clone, Copy, GridPosition)]
+pub struct Position {
+    pub x: i32,
+    pub y: i32,
+}
+
+impl<T: Into<(i32, i32)>> Add<T> for Position {
+    type Output = Self;
+
+    fn add(self, rhs: T) -> Self::Output {
+        let (dx, dy) = rhs.into();
+        Position {
+            x: self.x + dx,
+            y: self.y + dy,
+        }
+    }
+}
+
+impl<T: Into<(i32, i32)>> Sub<T> for Position {
+    type Output = Self;
+
+    fn sub(self, rhs: T) -> Self::Output {
+        let (dx, dy) = rhs.into();
+        Position {
+            x: self.x - dx,
+            y: self.y - dy,
+        }
+    }
+}
+
+impl Mul<i32> for Position {
+    type Output = Self;
+
+    fn mul(self, rhs: i32) -> Self::Output {
+        Position {
+            x: self.x * rhs,
+            y: self.y * rhs,
+        }
+    }
+}
+
+impl Position {
+    pub fn next(&self, direction: Direction) -> Self {
+        *self + direction
+    }
+
+    pub fn step(&mut self, direction: Direction) {
+        *self = self.next(direction);
+    }
+}
diff --git a/2023/10/src/puzzle.rs b/2023/10/src/puzzle.rs
diff --git a/Cargo.lock b/Cargo.lock
diff --git a/Cargo.toml b/Cargo.toml
diff --git a/direction/Cargo.toml b/direction/Cargo.toml
diff --git a/direction/src/lib.rs b/direction/src/lib.rs

-Original file line number
+Diff line change
@@ @@ -0,0 +1,5 @@ @@
 +.....
 +.S-7.
 +.|.|.
 +.L-J.
 +.....