int leds[] = {8,2,3,4,5,6,7,9,11,12};

int num = 10;

void setup() {
  Serial.begin(115200);

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

}

void loop() {
 for(int j = 0; j < num; j++){
  digitalWrite(leds[j], HIGH);
  delay(500);
  digitalWrite(leds[j], LOW);
 }
 
 for(int n = num -1; n>=0; n--){
  digitalWrite(leds[n], HIGH);
  delay(500);
  digitalWrite(leds[n], LOW);
 }

}