Eliminate the explicit grid

kifu/kifu-core/src/board.rs

@@ -10,7 +10,6 @@ pub enum Error {
 #[derive(Clone, Debug)]
 pub struct Board {
     pub size: Size,
-    pub grid: Grid<Option<Color>>,
     pub groups: Vec<Group>,
 }
 
@@ -45,7 +44,6 @@ impl Board {
                 width: 19,
                 height: 19,
             },
-            grid: Grid::new(19, 19),
             groups: Vec::new(),
         }
     }
@@ -90,11 +88,6 @@ impl Board {
         };
         self.groups.push(friendly_group.clone());
 
-        match self.grid.get_mut(coordinate.row, coordinate.column) {
-            None => return Err(Error::InvalidPosition),
-            Some(space) => *space = Some(color),
-        }
-
         let adjacent_groups = self.adjacent_groups(&friendly_group);
         for group in adjacent_groups {
             if self.liberties(&group) == 0 {
@@ -106,10 +99,10 @@ impl Board {
     }
 
     pub fn stone(&self, coordinate: &Coordinate) -> Option<Color> {
-        match self.grid.get(coordinate.row, coordinate.column) {
-            None => None,
-            Some(val) => *val,
-        }
+        self.groups
+            .iter()
+            .find(|g| g.contains(coordinate))
+            .map(|g| g.color)
     }
 
     pub fn group(&self, coordinate: &Coordinate) -> Option<&Group> {
@@ -120,12 +113,6 @@ impl Board {
 
     pub fn remove_group(&mut self, group: &Group) {
         self.groups.retain(|g| g != group);
-        for coord in group.coordinates.iter() {
-            match self.grid.get_mut(coord.row, coord.column) {
-                None => (),
-                Some(v) => *v = None,
-            }
-        }
     }
 
     pub fn adjacent_groups(&self, group: &Group) -> Vec<Group> {
@@ -263,6 +250,12 @@ pub struct Group {
     coordinates: HashSet<Coordinate>,
 }
 
+impl Group {
+    fn contains(&self, coordinate: &Coordinate) -> bool {
+        self.coordinates.contains(coordinate)
+    }
+}
+
 /*
 impl Group {
     pub fn adjacencies(&self, max_column: usize, max_row: usize) -> HashSet<Coordinate> {