const int LED_PINS[] = {13, 12, 14, 27, 26};
const int NUM_LEDS = 5;

void allOff() {
  for (int i = 0; i < NUM_LEDS; i++) {
    digitalWrite(LED_PINS[i], LOW);
  }
}

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

void loop() {
  for (int i = 0; i < NUM_LEDS; i++) {
    allOff();
    digitalWrite(LED_PINS[i], HIGH);
    delay(100);
  }
  for (int i = NUM_LEDS - 1; i >= 0; i--) {
    allOff();
    digitalWrite(LED_PINS[i], HIGH);
    delay(100);
  }
}