希尔排序

function shellSort(arr) {
  let temp
  let n = arr.length
  // `n >> 1` 相当于 `Math.floor(n / 2)`.
  for (let gap = n >> 1; gap > 0; gap = gap >> 1) {
    for (let i = gap; i < n; i++) {
      temp = arr[i]
      for (j = i - gap; j >= 0 && arr[j] > temp; j -= gap) {
        arr[j + gap] = arr[j]
      }
      arr[j + gap] = temp
    }
  }
  return arr
}