Add knight_moves_count to python lib

dotfiles/lib/python/knight_moves_count.py

@@ -0,0 +1,67 @@
+import sys
+
+
+class KnightMoves(object):
+
+    deltas = [(1, 2), (2, 1), (-1, 2), (-2, 1),
+              (1, -2), (2, -1), (-1, -2), (-2, -1)]
+
+    max_x = 8
+    max_y = 8
+
+    def count_knight_moves(self, start, end):
+        this_generation = [start]
+        move_count = 0
+        seen = set()
+
+        while True:
+            for position in this_generation:
+                if position in seen:
+                    continue
+                elif position == end:
+                    return move_count
+                else:
+                    seen.add(position)
+
+            this_generation = list(self.generate_moves_from_generation(this_generation))
+            move_count += 1
+
+    def generate_moves_from_generation(self, previous_generation):
+        return (
+            position
+            for ancestor in previous_generation
+            for position in self.generate_moves_from_position(ancestor)
+        )
+
+    def generate_moves_from_position(self, position):
+        x, y = position
+        return (
+            (x + delta_x, y + delta_y)
+            for delta_x, delta_y in self.deltas
+            if self.in_bounds(x + delta_x, y + delta_y)
+        )
+
+    def in_bounds(self, x, y):
+        return 0 <= x < self.max_x and 0 <= y < self.max_y
+
+
+def file_to_index(file_char):
+    assert 'a' <= file_char <= 'h'
+    return ord(file_char) - 97
+
+
+def rank_to_index(rank):
+    assert 0 < int(rank) <= 8
+    return int(rank) - 1
+
+
+def square_name_to_indices(square_name):
+    file_char, rank_char = square_name
+    return rank_to_index(int(rank_char)), file_to_index(file_char)
+
+
+if __name__ == '__main__':
+    print KnightMoves().count_knight_moves(
+        square_name_to_indices(sys.argv[1]),
+        square_name_to_indices(sys.argv[2])
+    )