// Withou usin delay
int ledState = 0; // Variable to keep track of the current LED state
unsigned long previousMillis = 0; // Variable to store the last time the LED was updated
const long interval = 500; // Interval at which to blink (milliseconds)

void setup() {
  // Set the pin modes
  pinMode(13, OUTPUT);
  pinMode(12, OUTPUT);
  pinMode(11, OUTPUT);
}

void loop() {
  unsigned long currentMillis = millis(); // Get the current time

  if (currentMillis - previousMillis >= interval) {
    // Save the last time you blinked the LED
    previousMillis = currentMillis;

    // Turn off all LEDs
    digitalWrite(13, LOW);
    digitalWrite(12, LOW);
    digitalWrite(11, LOW);

    // Update the LED state
    if (ledState == 0) {
      digitalWrite(13, HIGH);
      ledState = 1;
    } else if (ledState == 1) {
      digitalWrite(12, HIGH);
      ledState = 2;
    } else if (ledState == 2) {
      digitalWrite(11, HIGH);
      ledState = 0;
    }
  }
}