function simulate_game(starting_numbers, num_turns) {

  let last_visited_turn = {}

  for (let i = 0; i < starting_numbers.length; i++) {

    last_visited_turn[starting_numbers[i]] = i

  }

  starting_numbers.push(0)

  let starting_turn = starting_numbers.length - 1

  let next_value = starting_numbers[starting_turn]  

  let spoken_number = 0

  for (let turn = starting_turn; turn < num_turns; turn++) {

    spoken_number = next_value

    if (last_visited_turn[spoken_number] === undefined) {

      next_value = 0

    } else {

      next_value = turn - last_visited_turn[spoken_number]

    }

    last_visited_turn[spoken_number] = turn

  }

  return Object.keys(last_visited_turn).length

}

​

function simulate_game_2(startingList, limit) {

  let lastTurn = {}

  let turn = 1

  for (let i = 0; i < startingList.length; i++) {

    let n = startingList[i];

    lastTurn[n] = turn;

    turn++;

  }

​

  startingList.push(0)

  let lastNumber = startingList.slice(-1)[0];

  let newNumber = NaN;

​

  while (turn < limit) {

    if (lastTurn[lastNumber]) {

      newNumber = turn - lastTurn[lastNumber];

      lastTurn[lastNumber] = turn;

    } else {

      lastTurn[lastNumber] = turn;

      newNumber = 0;

    }

    lastNumber = newNumber;

    turn++;

  }

  return lastNumber

}

​

function setup() {

  let start = [6,19,0,5,7,13,1]

  print(simulate_game_2(start, 30000000))

}

​