该代码是实现聪明的贪食蛇的功能，规则如下，贪食蛇第一次碰墙后会自动向右转，第二次碰墙后会自动向左转，第三次碰墙后会反方向而行等。-The code is to achieve smart Snake features, the following rules, Snake will automatically turn to the right for the first time after touching the wall, it will automatically turn to the left after the second hit the wall, it will hit the wall after the third anti-the direction of the line and so on.