int t=100;
int i;
int pines[] ={2,4,5,18,19};
void setup() {

for(i=0;i<4; i++)
{
  pinMode(pines[i], OUTPUT);
}

}
void loop() 
{

for(i=0;i<4;i++){
digitalWrite(pines[i],HIGH);
delay(t);
digitalWrite(pines[i], LOW);
delay(t);
}

for(i=4;i>0;i--){
digitalWrite(pines[i],HIGH);
delay(t);
digitalWrite(pines[i], LOW);
delay(t);
}

}