const int leds[] = {2, 3, 4, 5, 6, 7, 8, 9};
bool direction = true;
int currentLED = 0;

void setup() {
  for (int i = 0; i < 8; i++) {
    pinMode(leds[i], OUTPUT);
  }
}

void loop() {
  digitalWrite(leds[currentLED], HIGH);
  delay(100);
  digitalWrite(leds[currentLED], LOW);

  if (direction) {
    currentLED++;
    if (currentLED == 7) {
      direction = false;
    }
  } else {
    currentLED--;
    if (currentLED == 0) {
      direction = true;
    }
  }
}