택배상자

export function courierBox(orders: number[]) {
  const stack = [];
  let [answer, current] = [0, 1];
 
  for (const order of orders) {
    while (current < order) {
      stack.push(current);
      current += 1;
    }
    if (order === current) {
      answer += 1;
      current += 1;
    } else if (stack.at(-1) === order) {
      answer += 1;
      stack.pop();
    } else {
      return answer;
    }
  }
 
  return answer;
}