const int pins[] = { 13 , 12 , 11};

void setup() {
  for( int i = 0 ; i < 3 ; i++){
    pinMode(pins[i] , OUTPUT);
  }

}
int counter = 0;
void loop() {

for(int i = 0 ; i < 3 ; i++){
  if(i == counter){
     digitalWrite(pins[i] , LOW);
  }
  else {
   digitalWrite(pins[i] , HIGH);
  }

}
delay(1000);
counter++;
 
if(counter > 2){
  counter = 0;
}

}