src/tasks/day13.rs

@@ -0,0 +1,148 @@
+use crate::utils;
+use std::collections::HashMap;
+
+pub fn task1() {
+    let (map, mut carts) = read_input();
+    println!("We have {} carts initially", carts.len());
+    loop {
+        perform_round(&map, &mut carts);
+    }
+}
+
+fn read_input() -> (Vec<Vec<char>>, Vec<Cart>) {
+    let input = utils::read_file("input/day13.txt");
+    let input: Vec<&str> = input.lines().collect();
+    let width = input[0].len();
+    let height = input.len();
+    let mut map = Vec::new();
+    let mut inner_vec = Vec::new();
+    inner_vec.resize(height, ' ');
+    map.resize(width, inner_vec);
+    let mut carts = Vec::new();
+    let tiles = vec!['|', '-', '/', '\\', '+'];
+    for (y, line) in input.iter().enumerate() {
+        for (x, c) in line.chars().enumerate() {
+            if tiles.contains(&c) {
+                map[x][y] = c;
+            } else {
+                if c != ' ' {
+                    map[x][y] = match c {
+                        '>' => '-',
+                        '<' => '-',
+                        '^' => '-',
+                        'v' => '-',
+                        _ => panic!("{} is invalid input char at this point", c),
+                    };
+                    carts.push(Cart {
+                        x,
+                        y,
+                        direction: c,
+                        intersections_visited: 0,
+                        active: true,
+                    });
+                }
+            }
+        }
+    }
+
+    (map, carts)
+}
+
+#[derive(Debug)]
+struct Cart {
+    x: usize,
+    y: usize,
+    direction: char,
+    intersections_visited: usize,
+    active: bool,
+}
+
+fn perform_round(map: &Vec<Vec<char>>, carts: &mut Vec<Cart>) {
+    carts.sort_unstable_by(|a, b| {
+        if a.y == b.y {
+            a.x.cmp(&b.x)
+        } else {
+            a.y.cmp(&b.y)
+        }
+    });
+    let mut positions: HashMap<(usize, usize), usize> = carts
+        .iter()
+        .enumerate()
+        .filter(|(_, cart)| cart.active)
+        .map(|(i, cart)| ((cart.x, cart.y), i))
+        .collect();
+
+    for cart_index in 0..carts.len() {
+        let mut cart = &mut carts[cart_index];
+        if !cart.active {
+            continue;
+        }
+
+        let pos_old = (cart.x, cart.y);
+        match cart.direction {
+            '>' => cart.x += 1,
+            '<' => cart.x -= 1,
+            '^' => cart.y -= 1,
+            'v' => cart.y += 1,
+            c => panic!("invalid direction {}", c),
+        }
+        cart.direction = match (cart.direction, map[cart.x][cart.y]) {
+            ('>', '/') => '^',
+            ('>', '\\') => 'v',
+            ('<', '/') => 'v',
+            ('<', '\\') => '^',
+            ('^', '/') => '>',
+            ('^', '\\') => '<',
+            ('v', '/') => '<',
+            ('v', '\\') => '>',
+            (direction, '+') => {
+                let new_direction = match cart.intersections_visited % 3 {
+                    0 => match direction {
+                        '>' => '^',
+                        '^' => '<',
+                        '<' => 'v',
+                        'v' => '>',
+                        _ => panic!("Invalid direction"),
+                    },
+                    1 => direction,
+                    2 => match direction {
+                        '>' => 'v',
+                        '^' => '>',
+                        '<' => '^',
+                        'v' => '<',
+                        _ => panic!("Invalid direction"),
+                    },
+                    _ => panic!("modulo 3 cannot be larger than 2"),
+                };
+                cart.intersections_visited += 1;
+                new_direction
+            }
+            (_, _) => cart.direction,
+        };
+        if positions.contains_key(&(cart.x, cart.y)) {
+            // Task1: panic here with coordinates
+            println!("We have a collision at {},{}!", cart.x, cart.y);
+            let other_index = positions[&(cart.x, cart.y)];
+            cart.active = false;
+            if !carts[other_index].active {
+                panic!("that one crashed already before!");
+            }
+            carts[other_index].active = false;
+            positions.remove(&(carts[cart_index].x, carts[cart_index].y));
+            positions.remove(&pos_old);
+            println!(
+                "{} carts left",
+                carts.iter().filter(|cart| cart.active).count()
+            );
+        } else {
+            positions.remove(&pos_old);
+            positions.insert((cart.x, cart.y), cart_index);
+        }
+    }
+    if carts.iter().filter(|cart| cart.active).count() == 1 {
+        panic!(
+            "exactly one active cart left: {:?}",
+            carts.iter().find(|cart| cart.active)
+        );
+    }
+}

src/tasks/mod.rs

@@ -10,3 +10,4 @@ pub mod day09;
 pub mod day10;
 pub mod day11;
 pub mod day12;
+pub mod day13;