src/day12/mod.rs

@@ -14,20 +14,20 @@ pub fn run() {
     let mut target: Coord = Default::default();
     let map = lines
         .enumerate()
-        .map(|(row, l)| {
+        .map(|(r, l)| {
             l.chars()
                 .enumerate()
                 .map(|(col, c)| match c {
                     'S' => {
                         start = Coord {
-                            row,
+                            row: r,
                             col,
                         };
                         0
                     }
                     'E' => {
                         target = Coord {
-                            row,
+                            row: r,
                             col,
                         };
                         25
@@ -45,7 +45,7 @@ pub fn run() {
 
     #[cfg(feature = "part2")]
     {
-        let min = map
+        let starting_points = map
             .iter()
             .enumerate()
             .flat_map(|(row, v)| {
@@ -58,6 +58,9 @@ pub fn run() {
                     })
                     .collect_vec()
             })
+            .collect_vec();
+        let min = starting_points
+            .iter()
             .filter_map(|start| bfs(&map, start.clone(), target.clone()))
             .min()
             .unwrap();
@@ -74,25 +77,48 @@ fn bfs(map: &Vec<Vec<u8>>, start: Coord, target: Coord) -> Option<usize> {
         if next == target {
             return Some(path_length);
         }
-        for coord in [(1, 0), (-1, 0), (0, 1), (0, -1)]
-            .iter()
-            .filter_map(|(dr, dc)|make_coord((next.row as isize) + dr, (next.col as isize) + dc, &map)) {
-            if map[next.row][next.col] + 1
-                < map[coord.row][coord.col] || visited[coord.row][coord.col] {
-                continue;
-            }
-            visited[coord.row][coord.col] = true;
-            queue.push_back((coord, path_length + 1));
+        match make_coord((next.row as isize) + 1, next.col as isize, &map, &visited) {
+            Some(down) if map[next.row][next.col] + 1
+                >= map[down.row][down.col] => {
+                visited[down.row][down.col] = true;
+                queue.push_back((down, path_length + 1));
+            },
+            _ => {}
+        }
+        match make_coord((next.row as isize) - 1, next.col as isize, &map, &visited) {
+            Some(up) if map[next.row][next.col] + 1
+                >= map[up.row][up.col] => {
+                visited[up.row][up.col] = true;
+                queue.push_back((up, path_length + 1));
+            },
+            _ => {}
+        }
+        match make_coord(next.row as isize, (next.col as isize) - 1, &map, &visited) {
+            Some(left) if map[next.row][next.col] + 1
+                >= map[left.row][left.col] => {
+                visited[left.row][left.col] = true;
+                queue.push_back((left, path_length + 1));
+            },
+            _ => {}
+        }
+        match make_coord(next.row as isize, (next.col as isize) + 1, &map, &visited) {
+            Some(right) if map[next.row][next.col] + 1
+                >= map[right.row][right.col] => {
+                visited[right.row][right.col] = true;
+                queue.push_back((right, path_length + 1));
+            },
+            _ => {}
         }
     }
     None
 }
 
-fn make_coord(row: isize, col: isize, map: &Vec<Vec<u8>>) -> Option<Coord> {
+fn make_coord(row: isize, col: isize, map: &Vec<Vec<u8>>, visited: &Vec<Vec<bool>>) -> Option<Coord> {
     if row >= 0
         && col >= 0
         && row < map.len() as isize
-        && (col as usize) < map[row as usize].len() {
+        && (col as usize) < map[row as usize].len()
+        && !visited[row as usize][col as usize] {
         Some(Coord {
             row: row as usize,
             col: col as usize