const int ledPins[] = {8, 9, 10, 11};
const int numLEDs = 4;

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

void loop() {
  // Forward direction
  for (int i = 0; i < numLEDs; i++) {
    digitalWrite(ledPins[i], HIGH);
    delay(200);
    digitalWrite(ledPins[i], LOW);
  }

  // Reverse direction
  for (int i = numLEDs - 2; i > 0; i--) { // skip first and last to avoid double blink
    digitalWrite(ledPins[i], HIGH);
    delay(200);
    digitalWrite(ledPins[i], LOW);
  }
}