int8_t piny[]={2,3,4,5,6,7,8,9,10,11};
int i=1;
int k=1;

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

void loop() {
  k=(i==0||i==10?-k:k);
  digitalWrite(piny[i], LOW);
  digitalWrite(piny[i+k], HIGH);
  i=i+k;
  delay(100);
}