Fast move validation

Author: USSiamaboat

board.py

@@ -282,6 +282,35 @@ def pick_one(s: set[int]) -> int:
         return (score[0], score[1])
 
 
+    def is_valid_move(self, row: int, col: int) -> bool:
+        # Compute stone value
+        val = self.move % 2 + 1
+
+        # Pass is always allowed
+        if (row, col) == (-1, -1):
+            return True
+        
+        # On top of another stone is never allowed
+        if self.grid[row, col] != 0:
+            return False
+        
+        # If capturing, needs play_stone
+        for group in self.groups:
+            if group.group_type == val:
+                continue
+            
+            if len(group - {(row, col)}) == 0:
+                return self.__play_stone(row, col, False)
+        
+        # Prohibit suicide
+        for group in self.groups:
+            if group.group_type == val:
+                continue
+
+            if len(group - {(row, col)}) == 0:
+                return False
+
+
     def play_stone(self, row: int, col: int, move: bool = True) -> bool:
         """
         Attempts to place a stone of value val at (row, col)
@@ -294,6 +323,23 @@ def play_stone(self, row: int, col: int, move: bool = True) -> bool:
             move (optional): whether or not to update the board, default True
         """
 
+        return self.__play_stone(row, col, move)
+
+
+    def __play_stone(self, row: int, col: int, move: bool = True) -> bool:
+        """
+        THIS IS A PRIVATE METHOD! DO NOT USE THIS OUTSIDE BOARD.PY
+
+        Attempts to place a stone of value val at (row, col)
+        
+        Returns True if the move is valid, False if not
+
+        Args:
+            row: index of the row to place the stone
+            col: index of the column to place the stone
+            move (optional): whether or not to update the board, default True
+        """
+
         # Compute stone value
         val = self.move % 2 + 1
 
@@ -363,18 +409,14 @@ def play_stone(self, row: int, col: int, move: bool = True) -> bool:
             if len(group.liberties) > 0:
                 new_candidate_groups.append(group)
                 continue
-
-            # Remove captured stones from the board
-            for i in group.intersections:
-                candidate[i // self.size, i % self.size] = 0
 
             # Record captures
             captured |= group.intersections
 
         # Update for newly opened intersections
         for group in candidate_groups:
             group.replenish_liberties(captured)
-        
+
         # Prohibit suicide
         for group in candidate_groups:
             # Skip opposite color
@@ -386,6 +428,10 @@ def play_stone(self, row: int, col: int, move: bool = True) -> bool:
 
             new_candidate_groups.append(group)
 
+        # Remove captured stones from the board
+        for i in captured:
+            candidate[i // self.size, i % self.size] = 0
+
         candidate_groups = new_candidate_groups
 
         # Prohibit repetition
@@ -430,10 +476,9 @@ def available_moves(self) -> list[tuple[int, int]]:
 
         for i in range(self.size):
             for j in range(self.size):
-                available = self.play_stone(
+                available = self.is_valid_move(
                     row = i,
-                    col = j,
-                    move = False
+                    col = j
                 )
 
                 if available:

game_node.py

@@ -89,10 +89,9 @@ def available_moves_mask(self) -> NDArray:
         out = np.zeros((self.size**2 + 1, ), dtype=bool)
 
         for i in range(self.size**2):
-            available = super().play_stone(
+            available = self.is_valid_move(
                 row = i // self.size,
                 col =  i % self.size,
-                move = False
             )
 
             if available:

group.py

@@ -92,10 +92,19 @@ def add_union(groups: list[Self], new_stone_group: Self) -> list[Self]:
                 out.append(group.copy())
 
         # Union groups of same stone containing the new stone as a liberty
-        unioned = Group(set(), set(), set(), new_stone_group.group_type)
-
-        for group in need_union:
-            unioned.union_in_place_(group)
+        new_intersections = set().union(*[group.intersections for group in need_union])
+        new_borders = set().union(*[group.borders for group in need_union])
+        new_liberties = set().union(*[group.liberties for group in need_union])
+
+        new_borders -= new_intersections
+        new_liberties -= new_intersections
+
+        unioned = Group(
+            intersections=new_intersections,
+            borders=new_borders,
+            liberties=new_liberties,
+            group_type=new_stone_group.group_type
+        )
 
         # Add unioned group back to group list
         out.append(unioned)