Merge pull request #986 from AInnuganti/distance

Add square_manhattan_distance and square_knight_distance functions

Author: niklasf

chess/__init__.py

@@ -218,10 +218,34 @@ def square_rank(square: Square) -> int:
 
 def square_distance(a: Square, b: Square) -> int:
     """
-    Gets the distance (i.e., the number of king steps) from square *a* to *b*.
+    Gets the Chebyshev distance (i.e., the number of king steps) from square *a* to *b*.
     """
     return max(abs(square_file(a) - square_file(b)), abs(square_rank(a) - square_rank(b)))
 
+def square_manhattan_distance(a: Square, b: Square) -> int:
+    """
+    Gets the Manhattan/Taxicab distance (i.e., the number of orthogonal king steps) from square *a* to *b*.
+    """
+    return abs(square_file(a) - square_file(b)) + abs(square_rank(a) - square_rank(b))
+
+def square_knight_distance(a: Square, b: Square) -> int:
+    """
+    Gets the Knight distance (i.e., the number of knight moves) from square *a* to *b*.
+    """
+    dx = abs(square_file(a) - square_file(b))
+    dy = abs(square_rank(a) - square_rank(b))
+
+    if dx + dy == 1:
+        return 3
+    elif dx == dy == 2:
+        return 4
+    elif dx == dy == 1:
+        if BB_SQUARES[a] & BB_CORNERS or BB_SQUARES[b] & BB_CORNERS: # Special case only for corner squares
+            return 4
+
+    m = math.ceil(max(dx / 2, dy / 2, (dx + dy) / 3))
+    return m + ((m + dx + dy) % 2)
+
 def square_mirror(square: Square) -> Square:
     """Mirrors the square vertically."""
     return square ^ 0x38

test.py

@@ -93,6 +93,31 @@ def test_parse_square(self):
         with self.assertRaises(ValueError):
             self.assertEqual(chess.parse_square("a0"))
 
+    def test_square_distance(self):
+        self.assertEqual(chess.square_distance(chess.A1, chess.A1), 0)
+        self.assertEqual(chess.square_distance(chess.A1, chess.H8), 7)
+        self.assertEqual(chess.square_distance(chess.E1, chess.E8), 7)
+        self.assertEqual(chess.square_distance(chess.A4, chess.H4), 7)
+        self.assertEqual(chess.square_distance(chess.D4, chess.E5), 1)
+
+    def test_square_manhattan_distance(self):
+        self.assertEqual(chess.square_manhattan_distance(chess.A1, chess.A1), 0)
+        self.assertEqual(chess.square_manhattan_distance(chess.A1, chess.H8), 14)
+        self.assertEqual(chess.square_manhattan_distance(chess.E1, chess.E8), 7)
+        self.assertEqual(chess.square_manhattan_distance(chess.A4, chess.H4), 7)
+        self.assertEqual(chess.square_manhattan_distance(chess.D4, chess.E5), 2)
+
+    def test_square_knight_distance(self):
+        self.assertEqual(chess.square_knight_distance(chess.A1, chess.A1), 0)
+        self.assertEqual(chess.square_knight_distance(chess.A1, chess.H8), 6)
+        self.assertEqual(chess.square_knight_distance(chess.G1, chess.F3), 1)
+        self.assertEqual(chess.square_knight_distance(chess.E1, chess.E8), 5)
+        self.assertEqual(chess.square_knight_distance(chess.A4, chess.H4), 5)
+        self.assertEqual(chess.square_knight_distance(chess.A1, chess.B1), 3)
+        self.assertEqual(chess.square_knight_distance(chess.A1, chess.C3), 4)
+        self.assertEqual(chess.square_knight_distance(chess.A1, chess.B2), 4)
+        self.assertEqual(chess.square_knight_distance(chess.C1, chess.B2), 2)
+
 
 class MoveTestCase(unittest.TestCase):