int led[] = {0,1,2,3,4,5,6,7,8,9};

void setup() {
  for(int i = 0; i <= 10; i++){
  pinMode(led[i], OUTPUT);
  }
  for(int j = 0; j <= 10; j++){
  pinMode(led[j], OUTPUT);
  }

}

void loop() {
  int i = 0;
  int j = 10;

  while(i < 6){
    digitalWrite(led[i], HIGH);
    digitalWrite(led[j], HIGH);
    delay(200);
    digitalWrite(led[i], LOW);
    digitalWrite(led[j], LOW);
    delay(100);
    i++;
    j--;
  }

  while(j > 6){
    digitalWrite(led[i], HIGH);
    digitalWrite(led[j], HIGH);
    delay(200);
    digitalWrite(led[i], LOW);
    digitalWrite(led[j], LOW);
    delay(100);
    i--;
    j++;
  }

  while(i > 6){
    digitalWrite(led[i], HIGH);
    digitalWrite(led[j], HIGH);
    delay(200);
    digitalWrite(led[i], LOW);
    digitalWrite(led[j], LOW);
    delay(100);
    i--;
    j++;
  }

  while(j < 6){
    digitalWrite(led[i], HIGH);
    digitalWrite(led[j], HIGH);
    delay(200);
    digitalWrite(led[i], LOW);
    digitalWrite(led[j], LOW);
    delay(100);
    i++;
    j--;
  }
  

}