#define PIN_RED 2     // The Arduino pin connected to R pin of traffic light module
#define PIN_YELLOW 3  // The Arduino pin connected to Y pin of traffic light module
#define PIN_GREEN 4   // The Arduino pin connected to G pin of traffic light module

#define RED_TIME 2000     // RED time in millisecond
#define YELLOW_TIME 1000  // YELLOW time in millisecond
#define GREEN_TIME 2000   // GREEN time in millisecond

#define RED    0  // Index in array
#define YELLOW 2  // Index in array
#define GREEN  1  // Index in array

const int pins[] = { PIN_RED, PIN_GREEN, PIN_YELLOW };
const int times[] = { RED_TIME, YELLOW_TIME, GREEN_TIME };
unsigned long last_time = 0;
int light = RED;  // start with RED light

void setup() {
  pinMode(PIN_RED, OUTPUT);
  pinMode(PIN_YELLOW, OUTPUT);
  pinMode(PIN_GREEN, OUTPUT);
  trafic_light_on(light);
  last_time = millis();
}

// the loop function runs over and over again forever
void loop() {
  if ((millis() - last_time) > times[light]) {
    light++;
    if (light >= 3)
      light = RED;  // new circle

    trafic_light_on(light);
    last_time = millis();
  }

  // TO DO: your other code
}

void trafic_light_on(int light) {
  for (int i = RED; i <= YELLOW; i++) {
    if (i == light)
      digitalWrite(pins[i], HIGH);  // turn on
    else
      digitalWrite(pins[i], LOW);  // turn off
  }
}