[lv. 0] 빈 배열에 추가, 삭제하기

function solution(arr, flag) {
  let answer = [];
  flag.map((f, i) => {
    if (f) {
      Array.from({length:arr[i]*2}, () => answer.push(arr[i]))
    }else {
      answer = answer.slice(0, -arr[i])
    }
  })
  return answer;
}