—Look, what an old palace! It looks so great!
—Yeah, it _______ nearly 800 years ago.
将一些棱长为1的正方体放在3×3的平面上如图1所示,其正视图,侧视图如下所示.若摆放的正方体的个数的最大值和最小值分别为m,n,则m-n=( )