const int NUM_LEDS = 10;
const int LED_PINS[NUM_LEDS] = {13, 12, 11, 10, 9, 8, 7, 6, 5, 4};

int count = 0;
int increment = 1;

void setup() {
  Serial.begin(115200);
  for (int i = 0; i < NUM_LEDS; i++)  {
    pinMode(LED_PINS[i], OUTPUT);
  }
}

void loop() {
  int potVal = analogRead(A0);
  int speed = map(potVal, 1023, 0, 100, 1000); // reverses pot
  // turn all LEDs off
  for (int i = 0; i < NUM_LEDS; i++)  {
    digitalWrite(LED_PINS[i], LOW);
  }
  // turn next LED on
  digitalWrite(LED_PINS[count], HIGH);
  count = count + increment;
  if (count <= 0) increment = 1;
  if (count >= (NUM_LEDS - 1)) increment = -1;
  // wait a little
  delay (speed);
}