September Morn Update

Task/Langtons-ant/Python/langtons-ant.py

@@ -1,28 +1,81 @@
-width = 75
-height = 52
-nsteps = 12000
+"""Langton's ant implementation."""
+from enum import Enum, IntEnum
 
-class Dir: up, right, down, left = range(4)
-class Turn: left, right = False, True
-class Color: white, black = '.', '#'
-M = [[Color.white] * width for _ in range(height)]
 
-x = width // 2
-y = height // 2
-dir = Dir.up
+class Dir(IntEnum):
+    """Possible directions."""
 
-i = 0
-while i < nsteps and 0 <= x < width and 0 <= y < height:
-    turn = Turn.left if M[y][x] == Color.black else Turn.right
-    M[y][x] = Color.white if M[y][x] == Color.black else Color.black
+    UP = 0
+    RIGHT = 1
+    DOWN = 2
+    LEFT = 3
 
-    dir = (4 + dir + (1 if turn else -1)) % 4
-    dir = [Dir.up, Dir.right, Dir.down, Dir.left][dir]
-    if   dir == Dir.up:    y -= 1
-    elif dir == Dir.right: x -= 1
-    elif dir == Dir.down:  y += 1
-    elif dir == Dir.left:  x += 1
-    else: assert False
-    i += 1
 
-print ("\n".join("".join(row) for row in M))
+class Color(Enum):
+    """Possible colors."""
+
+    WHITE = " "
+    BLACK = "#"
+
+
+def invert_color(grid, x, y):
+    """Invert the color of grid at x, y coordinate."""
+    if grid[y][x] == Color.BLACK:
+        grid[y][x] = Color.WHITE
+    else:
+        grid[y][x] = Color.BLACK
+
+
+def next_direction(grid, x, y, direction):
+    """Compute next direction according to current position and direction."""
+    if grid[y][x] == Color.BLACK:
+        turn_right = False
+    else:
+        turn_right = True
+    direction_index = direction.value
+    if turn_right:
+        direction_index = (direction_index + 1) % 4
+    else:
+        direction_index = (direction_index - 1) % 4
+    directions = [Dir.UP, Dir.RIGHT, Dir.DOWN, Dir.LEFT]
+    direction = directions[direction_index]
+    return direction
+
+
+def next_position(x, y, direction):
+    """Compute next position according to direction."""
+    if direction == Dir.UP:
+        y -= 1
+    elif direction == Dir.RIGHT:
+        x -= 1
+    elif direction == Dir.DOWN:
+        y += 1
+    elif direction == Dir.LEFT:
+        x += 1
+    return x, y
+
+
+def print_grid(grid):
+    """Display grid."""
+    print(80 * "#")
+    print("\n".join("".join(v.value for v in row) for row in grid))
+
+
+def ant(width, height, max_nb_steps):
+    """Langton's ant."""
+    grid = [[Color.WHITE] * width for _ in range(height)]
+    x = width // 2
+    y = height // 2
+    direction = Dir.UP
+
+    i = 0
+    while i < max_nb_steps and 0 <= x < width and 0 <= y < height:
+        invert_color(grid, x, y)
+        direction = next_direction(grid, x, y, direction)
+        x, y = next_position(x, y, direction)
+        print_grid(grid)
+        i += 1
+
+
+if __name__ == "__main__":
+    ant(width=75, height=52, max_nb_steps=12000)