残缺棋盘游戏问题；所谓残缺棋盘是指有一个格子残缺的棋盘。例如：
　　　　　　
　　　　　　
　　　　　　
　　　　　　
　　所谓三格板是指缺一个格子的2*2的棋盘。
　　给定一个2n*2n的残缺棋盘，问如何放置三格板，使得除残缺格外，棋盘中其他格子都被三格板覆盖，并且放置的三格板互不重叠。(The so-called three lattices are the 2*2 chessboards that are missing a lattice.　　　　　　Given the incomplete chessboard of a 2n*2n, ask how to place three grid panels, so that excepting the incomplete, the other checkerboard is covered by the three grid, and the three grid boards do not overlap each other.)