#define BUTTON 4
int LED[] = {5, 6, 9, 10, 11};

#define DELAY 100
#define STEP 50


bool isPressed() {
  // falling edge trigger
  static bool last = true;
  bool result = false;
  if (last && !digitalRead(BUTTON)) {
    result = true;
  }
  last = digitalRead(BUTTON);
  delay(1);
  return result;
}

void move() {
  static int clk = 0;
  for (int i = 0; i < 5; i++) {
    digitalWrite(LED[i], clk % 5 != i);
  }
  clk += 1;
}

void setup() {
  for (int i = 0; i < 5; i++) {
    pinMode(LED[i], OUTPUT);
    digitalWrite(LED[i], HIGH);
  }
  pinMode(BUTTON, INPUT);
}

void loop() {
  static int delay_time = DELAY;
  static bool stopping = false;
  static unsigned long checkpoint = 0;
  static int end = 0;
  static int step = 0;
  if (isPressed()) {
    stopping = !stopping;
    if (stopping) {
      end = random(12, 17);
      step = 0;
    } else {
      step = 0;
    }
  }

  if (millis() - checkpoint > delay_time) {
    if (!stopping || step < end) {
      move();
    }
    if (stopping) {
      step++;
    }
    checkpoint = millis();
  }
  delay_time = DELAY + step * STEP;
}