优雅的快速排序

func quickSort(arr []int, p, r int) {
    if p < r {
        q := partition(arr, p, r)
        quickSort(arr, p, q-1)
        quickSort(arr, q+1, r)
    }
}

func partition(arr []int, p, r int) int {
    //把最后一个值赋给x
    x := arr[r]
    i := p - 1
    for j := p; j <= r-1; j++ {
        if arr[j] <= x {
            i++
            arr[i], arr[j] = arr[j], arr[i]
        }
    }
    arr[i+1], arr[r] = arr[r], arr[i+1]
    return i + 1
}