struct LED {
  uint8_t const pin;
  unsigned long time;
};

unsigned long const timeout = 2000;
uint8_t const sensorPins[] = {13, 12, 11, 10, 9, 8, 7, 6};
LED leds[] = {{5, 0}, {4, 0}, {3, 0}, {2, 0}, {14, 0}, {15, 0}, {16, 0}};


template <class T, size_t N> arraySize(T (&)[N]) { return N; }


void setup() {
  for (uint8_t const& pin: sensorPins) {
    pinMode(pin, INPUT_PULLUP);
  }
  for (LED const& led: leds) {
    pinMode(led.pin, OUTPUT);
  }
}

void loop() {
  for (size_t i = 0; i < arraySize(sensorPins); i++) {
    if (not digitalRead(sensorPins[i])) {
      if (i) {
        digitalWrite(leds[i - 1].pin, HIGH);
        leds[i - 1].time = millis();
      }
      if (i < arraySize(leds)) {
        digitalWrite(leds[i].pin, HIGH);
        leds[i].time = millis();
      }
    }
  }
  for (LED const& led: leds) {
    if (millis() - led.time > timeout) {
      digitalWrite(led.pin, LOW);
    }
  }
}