quickSort.ts

const quickSort = (a: Array<number>): Array<number> => {
  if (a.length <= 1) {
    return a
  }
  const [n, ...ns] = a
  const { left, right } = ns.reduce<{ left: Array<number>; right: Array<number> }>(
    ({ left: left1, right: right1 }, m) => {
      if (m > n) {
        return { left: left1, right: right1.concat(m) }
      }
      return { left: left1.concat(m), right: right1 }
    },
    { left: [], right: [] },
  )
  return [...quickSort(left), n, ...quickSort(right)]
}