2 files changed, 179 insertions, 1 deletions
diff --git a/2018/src/day13.rs b/2018/src/day13.rs
new file mode 100644
index 0000000..13ff3a4
--- /dev/null
+++ b/2018/src/day13.rs
@@ -0,0 +1,176 @@
+use std::io;
+use std::io::BufRead;
+use std::collections::HashMap;
+
+#[derive(Clone, PartialEq, Eq, Hash)]
+struct Pos { x: usize, y: usize }
+
+#[derive(Clone)]
+struct Dir { x: i32, y: i32 }
+
+impl Dir {
+    fn rotright(&self) -> Dir {
+        Dir { x: -self.y, y: self.x }
+    }
+
+    fn rotleft(&self) -> Dir {
+        Dir { x: self.y, y: -self.x }
+    }
+}
+
+enum Choice {
+    Left,
+    Forward,
+    Right,
+}
+
+impl Choice {
+    fn incr(&mut self) {
+        match self {
+            Choice::Left => *self = Choice::Forward,
+            Choice::Forward => *self = Choice::Right,
+            Choice::Right => *self = Choice::Left,
+        }
+    }
+
+    fn apply(&self, dir: &Dir) -> Dir {
+        match self {
+            Choice::Left => dir.rotleft(),
+            Choice::Forward => dir.clone(),
+            Choice::Right => dir.rotright(),
+        }
+    }
+}
+
+struct Cart {
+    pos: Pos,
+    dir: Dir,
+    choice: Choice,
+}
+
+impl Cart {
+    fn nextpos(&self) -> Pos {
+        Pos { x: (self.pos.x as i32 + self.dir.x) as usize,
+              y: (self.pos.y as i32 + self.dir.y) as usize }
+    }
+}
+
+fn newdir(dir: &Dir, c: u8) -> Dir {
+    // println!(" newdir {},{} {}", dir.x, dir.y, std::char::from_u32(c as u32).unwrap());
+    if c == '|' as u8 || c == '-' as u8 {
+        Dir { x: dir.x, y: dir.y }
+    } else if c == '/' as u8 {
+        if dir.y == 0 {
+            dir.rotleft()
+        } else {
+            dir.rotright()
+        }
+    } else if c == '\\' as u8 {
+        if dir.y == 0 {
+            dir.rotright()
+        } else {
+            dir.rotleft()
+        }
+    } else {
+        println!("<{}>", c);
+        unreachable!();
+    }
+}
+
+fn print_dir(dir: &Dir) -> char {
+    match dir {
+        Dir{x:1,y:0} => '>',
+        Dir{x:-1,y:0} => '<',
+        Dir{x:0,y:1} => 'v',
+        Dir{x:0,y:-1} => '^',
+        Dir{..} => '?',
+    }
+}
+
+fn print_grid(grid: &Vec<Vec<u8>>, carts: &Vec<Cart>) {
+    let mut hascart: HashMap<Pos, usize> = HashMap::new();
+    for (i, cart) in carts.iter().enumerate() {
+        hascart.insert(cart.pos.clone(), i);
+    }
+
+    for y in 0..grid.len() {
+        for x in 0..grid[y].len() {
+            match hascart.get(&Pos { x, y }) {
+                Some(&idx) => {
+                    print!("{}", print_dir(&carts[idx].dir));
+                }
+                None => {
+                    print!("{}", std::char::from_u32(grid[y][x] as u32).unwrap());
+                }
+            }
+        }
+
+        println!("");
+    }
+}
+
+pub fn main<T: BufRead>(reader: T) -> io::Result<(String, String)> {
+    let mut grid: Vec<Vec<u8>> = reader.lines().map(|l| l.unwrap().as_bytes().to_vec()).collect();
+    let h = grid.len();
+    let w = grid[0].len();
+
+    let mut hascart = Vec::new();
+    for _ in 0..h {
+        hascart.push(vec![false; w]);
+    }
+
+    let mut carts: Vec<Cart> = Vec::new();
+    for y in 0..h {
+        for x in 0..w {
+            macro_rules! grid_process {
+                ( $c1:expr, $c2:expr, $dx:expr, $dy:expr ) => {
+                    if grid[y][x] == $c1 as u8 {
+                        grid[y][x] = $c2 as u8;
+                        carts.push(Cart { pos: Pos { x, y }, dir: Dir { x: $dx, y: $dy }, choice: Choice::Left });
+                        hascart[y][x] = true;
+                    }
+                }
+            }
+
+            grid_process!('>', '-', 1, 0);
+            grid_process!('<', '-', -1, 0);
+            grid_process!('^', '|', 0, -1);
+            grid_process!('v', '|', 0, 1);
+        }
+    }
+
+    let part1;
+
+    'outer: loop {
+        for mut cart in &mut carts {
+            let pos2 = cart.nextpos();
+            let c = grid[pos2.y][pos2.x];
+
+            // println!("cart at {},{} {},{}", cart.pos.x, cart.pos.y, cart.dir.x, cart.dir.y);
+
+            let dir2;
+            if c == '+' as u8 {
+                dir2 = cart.choice.apply(&cart.dir);
+                cart.choice.incr();
+            } else {
+                dir2 = newdir(&cart.dir, c);
+            }
+
+            if hascart[pos2.y][pos2.x] {
+                part1 = format!("{},{}", pos2.x, pos2.y);
+                break 'outer;
+            }
+
+            hascart[cart.pos.y][cart.pos.x] = false;
+            hascart[pos2.y][pos2.x] = true;
+            cart.pos = pos2;
+            cart.dir = dir2;
+        }
+
+        carts.sort_by_key(|cart| (cart.pos.y, cart.pos.x));
+
+        // print_grid(&grid, &carts);
+    }
+
+    Ok((part1, String::new()))
+}
diff --git a/2018/src/main.rs b/2018/src/main.rs
index daafaa4..27125d3 100644
--- a/2018/src/main.rs
+++ b/2018/src/main.rs
@@ -17,8 +17,9 @@ mod day9;
 mod day10;
 mod day11;
 mod day12;
+mod day13;
 
-static NUM_DAYS: i32 = 12;
+static NUM_DAYS: i32 = 13;
 
 fn day_switch<T: BufRead>(day: i32, reader: T) -> io::Result<(String, String)> {
     match day {
@@ -34,6 +35,7 @@ fn day_switch<T: BufRead>(day: i32, reader: T) -> io::Result<(String, String)> {
         10 => day10::main(reader),
         11 => day11::main(reader),
         12 => day12::main(reader),
+        13 => day13::main(reader),
         _ => Err(Error::new(ErrorKind::Other, "Invalid day"))
     }
 }