checkpoint

Cargo.lock

@@ -31,6 +31,13 @@ dependencies = [
  "winnow",
 ]
 
+[[package]]
+name = "day06"
+version = "0.1.0"
+dependencies = [
+ "winnow",
+]
+
 [[package]]
 name = "memchr"
 version = "2.7.4"

Cargo.toml

@@ -1,6 +1,6 @@
 [workspace]
 resolver = "2"
-members = ["day01", "day02", "day03", "day04", "day05"]
+members = ["day01", "day02", "day03", "day04", "day05", "day06"]
 
 [workspace.dependencies]
 winnow = "0.6"

day06/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "day06"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+winnow.workspace = true

day06/src/main.rs

@@ -0,0 +1,240 @@
+use std::{
+    collections::HashSet,
+    fmt::{Display, Write},
+};
+
+use winnow::{
+    PResult, Parser,
+    ascii::{newline, till_line_ending},
+    combinator::{alt, repeat, separated},
+};
+
+fn main() {
+    let input = std::fs::read_to_string("input").unwrap();
+    println!("{}", pt1(&input));
+    println!("{}", pt2(&input));
+}
+
+fn pt1(input: &str) -> usize {
+    let mut board = Board::new(input);
+
+    board.run()
+}
+
+fn pt2(input: &str) -> usize {
+    0
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
+enum Dir {
+    #[default]
+    N,
+    S,
+    E,
+    W,
+}
+
+impl Dir {
+    fn next(&self, loc: Loc) -> Loc {
+        let Loc(r, c) = loc;
+        let (nr, nc) = match self {
+            Dir::N => (r.wrapping_sub(1), c),
+            Dir::S => (r + 1, c),
+            Dir::E => (r, c + 1),
+            Dir::W => (r, c.wrapping_sub(1)),
+        };
+        Loc(nr, nc)
+    }
+
+    fn rot(&self) -> Self {
+        use Dir::*;
+        match self {
+            N => E,
+            E => S,
+            S => W,
+            W => N,
+        }
+    }
+}
+
+#[derive(Debug, Default, Clone, Copy, PartialEq, Eq, Hash)]
+struct Loc(usize, usize);
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum Cell {
+    Obstacle,
+    Empty,
+    Guard(Dir),
+    Visited,
+}
+
+impl Display for Cell {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        use Cell::*;
+        use Dir::*;
+        let c = match self {
+            Obstacle => '#',
+            Empty => '.',
+            Visited => 'X',
+            Guard(d) => match d {
+                N => '^',
+                E => '>',
+                S => 'v',
+                W => '<',
+            },
+        };
+        f.write_char(c)
+    }
+}
+
+#[derive(Debug, Default, Clone, PartialEq, Eq)]
+struct Board {
+    cells: Vec<Vec<Cell>>,
+    guard: (Loc, Dir),
+}
+
+impl Display for Board {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.write_str(
+            &self
+                .cells
+                .iter()
+                //.map(|row| row.iter().map(|c| format!("{c}")).collect::<String>())
+                .map(|row| {
+                    row.iter().fold(String::new(), |mut out, c| {
+                        let _ = write!(out, "{c}");
+                        out
+                    })
+                })
+                .collect::<Vec<_>>()
+                .join("\n"),
+        )
+    }
+}
+
+impl Board {
+    fn new(input: &str) -> Self {
+        parse(input).unwrap()
+    }
+
+    fn step(&mut self) -> Option<(Loc, Dir)> {
+        let (loc, dir) = &mut self.guard;
+        *self
+            .cells
+            .get_mut(loc.0)
+            .and_then(|r| r.get_mut(loc.1))
+            .unwrap() = Cell::Visited;
+        let nloc = dir.next(*loc);
+        if let Some(next_cell) = self
+            .cells
+            .get_mut(nloc.0)
+            .and_then(|row| row.get_mut(nloc.1))
+        {
+            match next_cell {
+                Cell::Obstacle => {
+                    *dir = dir.rot();
+                    Some((*loc, *dir))
+                }
+                Cell::Empty | Cell::Visited => {
+                    *next_cell = Cell::Guard(*dir);
+                    *loc = nloc;
+                    Some((nloc, *dir))
+                }
+                _ => unreachable!(),
+            }
+        } else {
+            None
+        }
+    }
+
+    fn run(&mut self) -> usize {
+        let mut locs = HashSet::new();
+        locs.insert(self.guard.0);
+        while let Some(loc) = self.step().map(|l| l.0) {
+            locs.insert(loc);
+        }
+        locs.len()
+    }
+}
+
+fn parse_cell(input: &mut &str) -> PResult<Cell> {
+    alt((parse_guard, parse_floor)).parse_next(input)
+}
+
+fn parse_guard(input: &mut &str) -> PResult<Cell> {
+    let g = alt(('^', '>', 'v', '<')).parse_next(input)?;
+    use Cell::Guard;
+    use Dir::*;
+    match g {
+        '^' => Ok(Guard(N)),
+        '>' => Ok(Guard(E)),
+        'v' | 'V' => Ok(Guard(S)),
+        '<' => Ok(Guard(W)),
+        _ => unreachable!(),
+    }
+}
+
+fn parse_floor(input: &mut &str) -> PResult<Cell> {
+    let g = alt(('.', '#')).parse_next(input)?;
+    match g {
+        '.' => Ok(Cell::Empty),
+        '#' => Ok(Cell::Obstacle),
+        'X' => Ok(Cell::Visited),
+        _ => unreachable!(),
+    }
+}
+
+fn parse_line(input: &mut &str) -> PResult<Vec<Cell>> {
+    let mut line = till_line_ending.parse_next(input)?;
+    repeat(1.., parse_cell).parse_next(&mut line)
+}
+
+fn parse(input: &str) -> PResult<Board> {
+    let mut gdir = Dir::N;
+    let mut loc = Loc(0, 0);
+
+    let mut input = input;
+    let cells: Vec<Vec<Cell>> = separated(1.., parse_line, newline)
+        .parse_next(&mut input)
+        .unwrap();
+
+    for (row, line) in cells.iter().enumerate() {
+        for (col, cell) in line.iter().enumerate() {
+            if let Cell::Guard(d) = cell {
+                gdir = *d;
+                loc = Loc(row, col);
+            }
+        }
+    }
+
+    Ok(Board {
+        cells,
+        guard: (loc, gdir),
+    })
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    static INPUT: &str = "....#.....
+.........#
+..........
+..#.......
+.......#..
+..........
+.#..^.....
+........#.
+#.........
+......#...";
+
+    #[test]
+    fn p1() {
+        let v = pt1(INPUT);
+        assert_eq!(v, 41)
+    }
+
+    #[test]
+    fn p2() {
+        assert_eq!(6, pt2(INPUT));
+    }
+}