const int numleds=4;
const int delayTime=250;

int ledPins[]={13,12,11,10};

void setup() {
  for(int i=0;i<numleds;i++){
   pinMode(ledPins[i],OUTPUT);
  } // put your setup code here, to run once:
}

void loop() {
  for(int i=0;i<numleds;i++) {
    digitalWrite(ledPins[i],HIGH);
    delay(delayTime);
    digitalWrite(ledPins[i],LOW);
}

 for( int i=numleds-1;i>=0;i-- ) {
    digitalWrite(ledPins[i],HIGH);
    delay(delayTime);
    digitalWrite(ledPins[i],LOW);
    }
}