don't re-parse every time

day06/src/main.rs

@@ -36,8 +36,9 @@ fn pt2(input: &str) -> usize {
         }
     }
 
+    let board = Board::new(input);
     for loc in trace {
-        board = Board::new(input);
+        let mut board = board.clone();
         let mut steps = HashSet::new();
         board.set(loc, Cell::Obstacle);
         steps.insert(board.guard);