棋盘拼接问题

接上一篇博客的问题：http://blog.csdn.net/zhang_xiaomeng/article/details/72954471

程序如下：

def cover(board, lab=1, top=0, left=0, side=None):    if side is None: side = len(board)    # Side length of subboard:    s = side // 2    # Offsets for outer/inner squares of subboards:    offsets = (0, -1), (side-1, 0)    for dy_outer, dy_inner in offsets:        for dx_outer, dx_inner in offsets:            # If the outer corner is not set...            if not board[top+dy_outer][left+dx_outer]:            # ... label the inner corner:                board[top+s+dy_inner][left+s+dx_inner] = lab    # Next label:    lab += 1    if s > 1:        for dy in [0, s]:            for dx in [0, s]:                # Recursive calls, if s is at least 2:                lab = cover(board, lab, top+dy, left+dx, s)                # Return the next available label:    return lab

运行：

>>> board = [[0]*8 for i in range(8)]>>> board[7][7] = -1>>> cover(board)22>>> for row in board:print((" %2i"*8) % tuple(row))  3  3  4  4  8  8  9  9  3  2  2  4  8  7  7  9  5  2  6  6 10 10  7 11  5  5  6  1  1 10 11 11 13 13 14  1 18 18 19 19 13 12 14 14 18 17 17 19 15 12 12 16 20 17 21 21 15 15 16 16 20 20 21 -1

程序分析如下：