Day 24, part 2

src/bin/d24p1.rs

@@ -8,6 +8,6 @@ pub fn main() {
 
     day24::print_map(&map, &start);
 
-    let rounds = day24::find_path(&map, &start, &target);
+    let (rounds, _) = day24::find_path(&map, &start, &target);
     println!("Goal is reachable in {} min", rounds);
 }

src/bin/d24p2.rs

@@ -0,0 +1,19 @@
+use aoc22::{
+    day24::{self},
+    util,
+};
+
+pub fn main() {
+    let (map, start, target) = day24::parse_map(&util::parse_input());
+
+    day24::print_map(&map, &start);
+
+    let (rounds_1, map_1) = day24::find_path(&map, &start, &target);
+    println!("Goal is reachable in {} min", rounds_1);
+    let (rounds_2, map_2) = day24::find_path(&map_1, &target, &start);
+    println!("Start is reachable in {} min", rounds_2);
+    let (rounds_3, _) = day24::find_path(&map_2, &start, &target);
+    println!("Goal is reachable in {} min", rounds_2);
+
+    println!("Total time taken is {} min", rounds_1 + rounds_2 + rounds_3);
+}

src/day24.rs

@@ -139,7 +139,15 @@ pub fn next_map(map: &Vec<Vec<Tile>>) -> Vec<Vec<Tile>> {
 }
 
 /// Returns length of the shortest path
-pub fn find_path(initial: &Vec<Vec<Tile>>, start: &Coord, target: &Coord) -> usize {
+pub fn find_path(
+    initial: &Vec<Vec<Tile>>,
+    start: &Coord,
+    target: &Coord,
+) -> (usize, Vec<Vec<Tile>>) {
+    let height = initial.len();
+    assert!(height > 0);
+    let width = initial[0].len();
+
     let mut map = initial.clone();
     let mut to_check = HashSet::new();
     to_check.insert(*start);
@@ -151,20 +159,23 @@ pub fn find_path(initial: &Vec<Vec<Tile>>, start: &Coord, target: &Coord) -> usi
         let mut check_next = HashSet::new();
 
         for pos in to_check {
-            let mut reachable = vec![
-                pos,
-                (pos.0 + 1, pos.1),
-                (pos.0, pos.1 + 1),
-                (pos.0, pos.1 - 1),
-            ];
-            // This would underflow in the first round
+            let mut reachable = vec![pos];
             if pos.0 != 0 {
                 reachable.push((pos.0 - 1, pos.1));
             }
+            if pos.0 != height - 1 {
+                reachable.push((pos.0 + 1, pos.1));
+            }
+            if pos.1 != 0 {
+                reachable.push((pos.0, pos.1 - 1));
+            }
+            if pos.1 != width - 1 {
+                reachable.push((pos.0, pos.1 + 1));
+            }
 
             for p in reachable {
                 if p == *target {
-                    return rounds;
+                    return (rounds, map);
                 }
                 if matches!(map[p.0][p.1], Tile::Empty) {
                     check_next.insert(p);