int BUTTON_UP = 2;
int BUTTON_DOWN = 4;
int BUTTON_LEFT = 3;
int BUTTON_RIGHT = 5;
int LED0 = 18;
int LED1 = 19;
int LED2 = 22;
int LED3 = 23;
int LED4 = 10;
int LED5 = 11;
int LED6 = 16;
int LED7 = 17;
int LED8 = 7;
int LED9 = 6;
int LED10 = 8;
int LED11 = 9;

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600); 
  pinMode(LED0, OUTPUT);
  pinMode(LED1, OUTPUT);
  pinMode(LED2, OUTPUT);
  pinMode(LED3, OUTPUT);
  pinMode(LED4, OUTPUT);
  pinMode(LED5, OUTPUT);
  pinMode(LED6, OUTPUT);
  pinMode(LED7, OUTPUT);
  pinMode(LED8, OUTPUT);
  pinMode(LED9, OUTPUT);
  pinMode(LED10, OUTPUT);
  pinMode(LED11, OUTPUT);
  pinMode(BUTTON_UP, INPUT_PULLUP);
  pinMode(BUTTON_DOWN, INPUT_PULLUP);
  pinMode(BUTTON_LEFT, INPUT_PULLUP);
  pinMode(BUTTON_RIGHT, INPUT_PULLUP);
}

typedef struct { 
  int ledIndex;
  int ledPin;
} ledMap;

const ledMap myLedMap[] {
    {0, LED0},
    {1, LED1},
    {2, LED2},
    {3, LED3},
    {4, LED4},
    {5, LED5},
    {6, LED6},
    {7, LED7},
    {8, LED8},
    {9, LED9},
    {10, LED10},
    {11, LED11}
};

int currLEDIndex = 0;
int delay_time = 500;
int prevButtonState = 1;
int currButtonState = 1;

void loop() {
  // put your main code here, to run repeatedly:
  int ledPin = myLedMap[currLEDIndex].ledPin;
  digitalWrite(ledPin, HIGH);
  delay(delay_time);
  digitalWrite(ledPin, LOW);
  currLEDIndex = (currLEDIndex + 1) % 12;

  prevButtonState = currButtonState;
  currButtonState = digitalRead(BUTTON_UP);
  if((currButtonState != prevButtonState) && (currButtonState == LOW)){
    delay_time = delay_time / 2;
    if (delay_time < 25) {
      delay_time = 25;
    }
    return;
  }
  currButtonState = digitalRead(BUTTON_DOWN);
  if((currButtonState != prevButtonState) && (currButtonState == LOW)){
    delay_time = delay_time * 2;
    return;
  }
}