1.设计一个十字路口交通信号灯控制器，其要求如下：
设南北方向的红、黄、绿灯分别为r，y，g；东西方向的红、黄、绿灯分别为R，Y，G，满足图1 的工作流程并且可以并行工作：g（R）→r（G），黄灯用于提示绿灯变为红灯或者绿灯变为红灯。(1. Designing a traffic light controller for intersections, the requirements are as follows:

Let the red, yellow and green lights in the north and south directions be r, y and G respectively; the red, yellow and green lights in the East and west directions are R, Y and G respectively, which meet the working flow of Figure 1 and can work concurrently: g (R)r (G). The yellow light is used to prompt the green light to turn into a red light or a green light to turn into a red light.)