const int ledPins[] = {2, 3, 4, 5}; // RED GREEN YELLOW BLUE 
const int buttonPins[] = {6, 7, 8, 9};  // RED GREEN YELLOW BLUE 
unsigned long startTime;
int userTime = 0;
int userInput = -1;
int lightedLed = 0;

void setup() {
  for (int i = 0; i < 4; i++) {
    pinMode(ledPins[i], OUTPUT);
    pinMode(buttonPins[i], INPUT_PULLUP);
  }
  Serial.begin(9600);
}

void loop() {
  lightRandomLed();
  while (!checkUserInput());
}

int generateRandomTime1To3() {
  return ((random() % 3) + 1);
}

void lightRandomLed() {
  delay(generateRandomTime1To3() * 1000);
  lightedLed = random() % 4;
  digitalWrite(ledPins[lightedLed], HIGH);
  startTime = millis();
}

boolean checkUserInput() {
  for (int i = 0; i < 4; i++) {
    if (digitalRead(buttonPins[i]) == LOW) {
      userInput = i;
    }
  }
  if (userInput == lightedLed) {
    userTime = millis() - startTime;
    digitalWrite(ledPins[lightedLed], LOW);
    Serial.print("Your Score is:");
    Serial.print(userTime / 1000.0);
    userInput = -1;
    Serial.println(" Second");
    return true;
  }
  return false;
}