int rows[] = {0, 1};
int columns[] = {2, 3, 4};
int pins[] = {14, 15, 16, 17, 18, 19};

void setup() {
  for (int i = 0; i < 2; i++) {
    pinMode(i, INPUT_PULLUP);
  }
  
  pinMode(13, OUTPUT);
  
  for (int i=0; i<6; i++) {
    pinMode(pins[i], OUTPUT);
  }
}

bool key_pressed(const int key) {
  const int row = key / 3;
  const int column = key % 3;

  pinMode(columns[column], OUTPUT);
  digitalWrite(columns[column], LOW);
  bool pressed = digitalRead(rows[row]) == LOW;
  pinMode(columns[column], INPUT);

  return pressed;
}

void loop() {
  digitalWrite(13, HIGH);
  for (int i=0; i<6; i++) {
    if (key_pressed(i)) {
      digitalWrite(pins[i], HIGH);
    } else {
      digitalWrite(pins[i], LOW);
    }
  }
}