add bounding area score to solution results

src/marble_engine/grid.rs

@@ -123,6 +123,48 @@ impl Grid {
 		sum
 	}
 
+	pub fn used_bounds_area(&self) -> usize {
+		let row_clear = |a, max, f: fn(usize, usize) -> (usize, usize)| {
+			for b in 0..max {
+				if !self.get_unchecked(f(a, b).into()).is_blank() {
+					return false;
+				}
+			}
+			true
+		};
+		let mut height = self.height;
+		for y in 0..self.height {
+			if row_clear(y, self.width, |y, x| (x, y)) {
+				height -= 1;
+			} else {
+				break;
+			}
+		}
+		for y in (0..self.height).rev() {
+			if row_clear(y, self.width, |y, x| (x, y)) {
+				height -= 1;
+			} else {
+				break;
+			}
+		}
+		let mut width = self.width;
+		for x in 0..self.width {
+			if row_clear(x, self.height, |x, y| (x, y)) {
+				width -= 1;
+			} else {
+				break;
+			}
+		}
+		for x in (0..self.width).rev() {
+			if row_clear(x, self.width, |x, y| (x, y)) {
+				width -= 1;
+			} else {
+				break;
+			}
+		}
+		width * height
+	}
+
 	fn in_bounds(&self, p: Pos) -> bool {
 		p.x >= 0 && p.y >= 0 && p.x < self.width as PosInt && p.y < self.height as PosInt
 	}