const int pindiod[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9 }; 
const int diodnumber = 9; 

void setup()
{
  for(int a = 0; a < diodnumber; a++)
    {
      pinMode(pindiod[a], OUTPUT);  
    } 
}

void loop() 
{ 
  for (int a = 0; a < (diodnumber -1) / 2; a++) 
    {
      digitalWrite(pindiod[a], true);
      digitalWrite(pindiod[diodnumber -1 -a], true);
      delay(500); 
      digitalWrite(pindiod[a], !true); 
      digitalWrite(pindiod[diodnumber -1 -a], !true); 
    }
      digitalWrite(pindiod[diodnumber / 2], true);
      digitalWrite(pindiod[diodnumber / 2], !true);
  for (int a = (diodnumber -1) / 2 ; a >= 0; a--) 
    {
      digitalWrite(pindiod[a], true);
      digitalWrite(pindiod[diodnumber -1 -a], true);
      delay(500); 
      digitalWrite(pindiod[a], !true); 
      digitalWrite(pindiod[diodnumber -1 -a], !true); 
    } 
      delay(500);     
}