Xmas Tree lights project for MakeUseOf.com

int leds[] = {2,3,4,5,6,7,8,9,10}; // 9 total

void setup(){
   for(int i = 0;i<90;i++){
       pinMode(leds[i],OUTPUT);
   }
}

void loop(){
   oneAtATime();
   //randomSequence();
   //topToBottom();
}
// Turns each LED off one at a time
void oneAtATime(){
  for(int i = 0;i< 9;i++){
      digitalWrite(leds[i],HIGH);
      delay(100);
      digitalWrite(leds[i],LOW);
   }
}

// utterly random , a a kind of twinkling effect is acheived?
void randomSequence(){

  int randomLed = random(0,9);
  digitalWrite(leds[randomLed],HIGH);
      delay(50);

  randomLed = random(0,9);
  digitalWrite(leds[randomLed],LOW);

}

// HOMEWORK: This one goes from top to bottom
void topToBottom(){
  int d = 100;

  for(int i = 0;i< 5;i++){
     digitalWrite(leds[4-i],HIGH);
     digitalWrite(leds[4+i],HIGH);
     delay(d);
     digitalWrite(leds[4+i],LOW);
     digitalWrite(leds[4-i],LOW);
     delay(d);

   }

   for(int i = 4;i> 0;i--){
     digitalWrite(leds[4-i],HIGH);
     digitalWrite(leds[4+i],HIGH);
     delay(d);
     digitalWrite(leds[4+i],LOW);
     digitalWrite(leds[4-i],LOW);
     delay(d);

   }

}