// L1-005 三灯双向流水灯（往返流水）教师完整版
// 引脚定义
const int ledRed   = 13;
const int ledYellow= 12;
const int ledGreen = 11;

// 初始化：全部配置为输出
void setup() {
  pinMode(ledRed, OUTPUT);
  pinMode(ledYellow, OUTPUT);
  pinMode(ledGreen, OUTPUT);
}

void loop() {
  // ========== 【正向流水：红 → 黄 → 绿】 ==========
  // 红灯亮
  digitalWrite(ledRed, HIGH);
  digitalWrite(ledYellow, LOW);
  digitalWrite(ledGreen, LOW);
  delay(500);

  // 黄灯亮
  digitalWrite(ledRed, LOW);
  digitalWrite(ledYellow, HIGH);
  digitalWrite(ledGreen, LOW);
  delay(500);

  // 绿灯亮
  digitalWrite(ledRed, LOW);
  digitalWrite(ledYellow, LOW);
  digitalWrite(ledGreen, HIGH);
  delay(500);

  // ========== 【反向流水：绿 → 黄 → 红】 ==========
  // 绿灯保持（衔接终点，不跳转断层）
  // 黄灯亮
  digitalWrite(ledRed, LOW);
  digitalWrite(ledYellow, HIGH);
  digitalWrite(ledGreen, LOW);
  delay(500);

  // 红灯亮
  digitalWrite(ledRed, HIGH);
  digitalWrite(ledYellow, LOW);
  digitalWrite(ledGreen, LOW);
  delay(500);
}