338.md

看了提示写出来的

const countBits = function (num) {
  let res = [], count = 0, str = '';
  for (let i = 0; i <= num; ++i) {
    let n = i;
    while (n !== 0) {
      if (res[n]) {
        count += res[n];
        break;
      }
      if (n % 2 === 1) {
        ++count;
      }
      n = parseInt(n / 2);
    }
    res[i] = count;
    count = 0;
  }
  return res;
};

评论区很棒的解法 f[8] = f[4] + 8的最后一位是不是1,因为移位会把最后一位挤出去,所以要判断下最后一位;

const countBits = function (num) {
  let f = [0], count = 0, str = '';
  for (let i=1; i<=num; i++) f[i] = f[i >> 1] + (i & 1);
  return f;
};