有一m*n的棋盘(即棋盘由m行和n列)，一马放在棋盘中任意位置，马按中国象棋跳法，从初始位置起跳，跳至边界后返回，求所有能返回初始位置的周游路线。(A m*n board (the board consists of M rows and N columns), a horse placed anywhere in the board, according to the China chess horse jump method, from the initial position jump,