// Define the number of LEDs
#define NUM_LEDS 20

// Define the pin number for the LEDs
const int ledPins[NUM_LEDS] = {0, 1 ,2, 3, 4, 5, 6, 7, 8, 9, 10, 11,
                                12, 13, A0, A1, A2, A3, A4, A5};

// Define the delay time between each LED
const int delayTime = 500;

void setup() {
  // Initialize the LED pins as OUTPUT
  for (int i = 0; i < NUM_LEDS; i++) {
    pinMode(ledPins[i], OUTPUT);
  }
}

void loop() {
  // Turn on each LED in sequence
  for (int i = 0; i < NUM_LEDS; i++) {
    digitalWrite(ledPins[i], HIGH);  // Turn on the LED
    delay(delayTime);                // Delay
    digitalWrite(ledPins[i], LOW);   // Turn off the LED
  }

  // Turn off all LEDs
  for (int i = 0; i < NUM_LEDS; i++) {
    digitalWrite(ledPins[i], LOW);
  }

  // Reverse the direction and repeat
  for (int i = NUM_LEDS - 1; i >= 0; i--) {
    digitalWrite(ledPins[i], HIGH);  // Turn on the LED
    delay(delayTime);                // Delay
    digitalWrite(ledPins[i], LOW);   // Turn off the LED
  }

  // Turn off all LEDs
  for (int i = 0; i < NUM_LEDS; i++) {
    digitalWrite(ledPins[i], LOW);
  }
}