设有一个十字路口，1、3为南，北方向， 2、4为东，西方向。 初始化之后， 1、3路口的绿灯亮， 2、4路口的红灯亮， 1、3路口方向通车。 延迟一段时间（30秒）后， 1、3路口的绿灯熄灭，而1、3路口的黄灯开始闪烁。闪烁3次（延时3秒）后， 1、3路口的红灯亮， 同时2、4路口的绿灯亮， 2、4路口方向开始通车。 延迟一段时间（30秒）后， 2、4路口的绿灯熄灭，而黄灯开始闪烁。闪烁3次（延时3秒）后，再切换到1、3路口方向。 之后，重复上述过程(There is a crossroad, 1 and 3 are South and North, 2 and 4 are East and West. After initialization, the green lights on the 1 and 3 crossings are bright, the red light on the 2 and the 4 crossings, and the direction of the 1 and 3 intersection. After a period of 30 seconds (30 seconds), the green lights of the 1 and 3 intersections go out, and the yellow lights at the 1 and 3 junctions start to flicker. After flashing 3 times (delay 3 seconds), the red light of the 1 and 3 intersection is bright, and the green lights of the 2 and 4 junctions are bright, and the 2, 4 crossing directions begin to open. After a period of time (30 seconds), the green lights of the 2 and 4 intersections go out, and the yellow lights start to flicker. After flashing 3 times (time delay 3 seconds), then switch to the direction of the 1 and 3 intersection. After that, repeat the above process)