回朔算法，马的周游问题：在n x n棋盘（有n x n个格点的棋盘）的某个格点上有一个中国象棋马，马走日字。求一条周游棋盘的路径，使得马能够从起始位置起沿着该路径每个格点恰好走一次最后回到出发位置。-Retrospective algorithm, horse around the problem: in the checkerboard are like (there are like a checkerboard grid points) of a grid, there is a Chin