1 files changed, 4 insertions, 1 deletions

diff --git a/2023/src/day21.cpp b/2023/src/day21.cpp
index 21a45f7..88fafec 100644
--- a/2023/src/day21.cpp
+++ b/2023/src/day21.cpp
@@ -38,6 +38,9 @@ find_neighbours(position pos, const vector<string>& lines)
 {
         static const vector<position> movements = { { -1, 0 }, { 0, 1 }, { 1, 0 }, { 0, -1 } };
 
+        const auto height = lines.size();
+        const auto width  = lines[0].size();
+
         set<position> neighbours;
         const auto [row, col] = pos;
 
@@ -45,7 +48,7 @@ find_neighbours(position pos, const vector<string>& lines)
                 const auto nrow = row + drow;
                 const auto ncol = col + dcol;
 
-                if ( nrow < lines.size() && ncol < lines[0].size() && (lines[nrow][ncol] == '.' || lines[nrow][ncol] == 'S') ) {
+                if ( nrow < height && ncol < width && lines[nrow][ncol] != '#' ) {
                         neighbours.emplace(nrow, ncol);
                 }
         }