day17: don't revisit the start position

17/src/main.rs

@@ -311,6 +311,7 @@ impl<'a> WalkCost2<'a> {
                             weight: cur_move.weight + self.map.map[new_pos.1][new_pos.0],
                         })
                     })
+                    .filter(|m| m.new_pos != self.start)
                     .filter(|m| *m.dir != cur_move.dir.opposite())
                     .filter(|m| {
                         if m.dir == cur_move.dir {