#define  FIRST_LED 27
#define  SECOND_LED 32
#define  THIRD_LED 33
#define  FOURTH_LED 25
#define  FIFTH_LED 26
#define  SIXTH_LED 5
#define  SEVENTH_LED 17
#define  EIGHTH_LED 16
#define delay_var 50

const int led_list[] = {
  FIRST_LED,
  SECOND_LED,
  THIRD_LED,
  FOURTH_LED,
  FIFTH_LED,
  SIXTH_LED,
  SEVENTH_LED,
  EIGHTH_LED,
};

const int num_leds = sizeof(led_list) / sizeof(led_list[0]);

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

void loop() {
  for(int i = 0; i < num_leds; i++) {
    digitalWrite(led_list[i], HIGH);  
    delay(delay_var);       
    digitalWrite(led_list[i], LOW);   
    delay(delay_var);  
  }

  for(int i = num_leds - 1; i >= 0; i--) {
    digitalWrite(led_list[i], HIGH);
    delay(delay_var);
    digitalWrite(led_list[i], LOW);
    delay(delay_var);
  }

  for(int i = 0; i < num_leds / 2; i++) {
    digitalWrite(led_list[num_leds / 2 - 1 - i], HIGH);
    digitalWrite(led_list[num_leds / 2 + i], HIGH);
    delay(delay_var);
    digitalWrite(led_list[num_leds / 2 - 1 - i], LOW);
    digitalWrite(led_list[num_leds / 2 + i], LOW);
    delay(delay_var);
  }

  for(int i = 0; i < num_leds / 2; i++) {
    digitalWrite(led_list[i], HIGH);
    digitalWrite(led_list[num_leds - 1 - i], HIGH);
    delay(delay_var);
    digitalWrite(led_list[i], LOW);
    digitalWrite(led_list[num_leds - 1 - i], LOW);
    delay(delay_var);
  }
}