Day 12, puzzle 2

src/bin/d12p1.rs

@@ -3,7 +3,7 @@ use aoc22::{day12, util};
 pub fn main() {
     let heightmap = day12::parse_heightmap(&util::parse_input());
 
-    let dist = day12::path_steps(&heightmap).expect("No path found!?");
+    let dist = day12::path_steps(&heightmap, false).expect("No path found!?");
 
     println!("Distance to target is {}", dist);
 }

src/bin/d12p2.rs

@@ -0,0 +1,9 @@
+use aoc22::{day12, util};
+
+pub fn main() {
+    let heightmap = day12::parse_heightmap(&util::parse_input());
+
+    let dist = day12::path_steps(&heightmap, true).expect("No path found!?");
+
+    println!("Distance to target is {}", dist);
+}

src/day12.rs

@@ -59,19 +59,20 @@ pub fn parse_heightmap(input: &String) -> Heightmap {
     }
 }
 
-pub fn path_steps(map: &Heightmap) -> Option<usize> {
+pub fn path_steps(map: &Heightmap, any_a: bool) -> Option<usize> {
     let mut dist = vec![vec![usize::MAX; map.cols]; map.rows];
-    dist[map.start.0][map.start.1] = 0;
+    dist[map.target.0][map.target.1] = 0;
     let mut next = VecDeque::new();
-    next.push_back(map.start);
+    next.push_back(map.target);
 
     let moves: Vec<(isize, isize)> = vec![(1, 0), (-1, 0), (0, 1), (0, -1)];
     while let Some(coord) = next.pop_front() {
-        if coord == map.target {
-            break;
-        }
         let curr_height = map.map[coord.0][coord.1];
         let curr_dist = dist[coord.0][coord.1];
+        if curr_height == 0 && (any_a || coord == map.start) {
+            return Some(curr_dist);
+        }
+
         for move_ in &moves {
             let y = (coord.0 as isize) + move_.0;
             if y < 0 || y >= map.rows as isize {
@@ -83,17 +84,12 @@ pub fn path_steps(map: &Heightmap) -> Option<usize> {
             }
             let y = y as usize;
             let x = x as usize;
-            if map.map[y][x] <= curr_height + 1 && dist[y][x] > curr_dist + 1 {
+            if map.map[y][x] + 1 >= curr_height && dist[y][x] > curr_dist + 1 {
                 dist[y][x] = curr_dist + 1;
                 next.push_back((y, x));
             }
         }
     }
 
-    let d = dist[map.target.0][map.target.1];
-    if d < usize::MAX {
-        Some(d)
-    } else {
-        None
-    }
+    None
 }