#define N 9
int LED[N] = {1,2,3,4,5,6,7,8,9};
int prev = LED[N-1]; // previous 이전
//int curr_LED = LED[N-1]; // current 현재

void clear_LED()
{
  for(int i = 0; i < N; i++)
  {
    digitalWrite(LED[i], LOW);
  }
}

void setup() {
  for( int i = 0; i < N; i++)
  {
    pinMode(LED[i], OUTPUT);
  }
  clear_LED();
}

void loop() {
  for(int i = 0; i < N; i++)
  {
    digitalWrite(prev, LOW);

    int j = (N-1) - i;
    digitalWrite(LED[j], HIGH);
    delay(25);

    clear_LED();
    delay(100);

    int x = i;
    digitalWrite(LED[x], HIGH);
    delay(25);
  }
}