const int pin_red = 13;
const int pin_yellow = 12;
const int pin_green = 11;

enum State_t{
  red, yellow, green
};
State_t curr_state;
State_t prev_state;


void setup() {
  // put your setup code here, to run once:
  pinMode(pin_red, OUTPUT); //red
  pinMode(pin_yellow, OUTPUT); //yellow
  pinMode(pin_green, OUTPUT); //green
  curr_state = red;
  prev_state = red;
}

void loop() {
  // put your main code here, to run repeatedly:
  switch(curr_state){
    case red: 
      digitalWrite(pin_red, HIGH);
      delay(5000);
      digitalWrite(pin_red, LOW);
      curr_state = yellow;
      prev_state = red;
      break;
    case yellow:
      digitalWrite(pin_yellow, HIGH);  
      delay(1000);
      digitalWrite(pin_yellow, LOW);
      if(prev_state == green){
        curr_state = red;
      }
      else{
        curr_state = green;
      }
      break;
    case green:
      digitalWrite(pin_green, HIGH);
      delay(5000);
      digitalWrite(pin_green, LOW);
      curr_state = yellow;
      prev_state = green;
      break;
  }
}