day13 part2

src/tasks/day13.rs

@@ -1,8 +1,9 @@
 use crate::utils;
-use std::collections::HashSet;
+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);
     }
@@ -37,6 +38,7 @@ fn read_input() -> (Vec<Vec<char>>, Vec<Cart>) {
                         y,
                         direction: c,
                         intersections_visited: 0,
+                        active: true,
                     });
                 }
             }
@@ -46,11 +48,13 @@ fn read_input() -> (Vec<Vec<char>>, Vec<Cart>) {
     (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>) {
@@ -61,10 +65,19 @@ fn perform_round(map: &Vec<Vec<char>>, carts: &mut Vec<Cart>) {
             a.y.cmp(&b.y)
         }
     });
-    let mut positions: HashSet<(usize, usize)> =
-        carts.iter().map(|cart| (cart.x, cart.y)).collect();
+    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;
+        }
 
-    for cart in carts {
         let pos_old = (cart.x, cart.y);
         match cart.direction {
             '>' => cart.x += 1,
@@ -106,11 +119,30 @@ fn perform_round(map: &Vec<Vec<char>>, carts: &mut Vec<Cart>) {
             }
             (_, _) => cart.direction,
         };
-        if positions.contains(&(cart.x, cart.y)) {
-            panic!("We have a collision at {},{}!", cart.x, cart.y);
+        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));
+            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)
+        );
+    }
 }