如何将字符串从大到小排序

def sort_string_descending(string):
    # 将字符串转换为字符数组
    char_array = list(string)

    # 快速排序算法
    def quick_sort(array, start, end):
        if start >= end:
            return
        pivot = array[start]
        left = start + 1
        right = end
        while left <= right:
            if array[left] < pivot and array[right] > pivot:
                array[left], array[right] = array[right], array[left]
            if array[left] >= pivot:
                left += 1
            if array[right] <= pivot:
                right -= 1
        array[start], array[right] = array[right], array[start]
        quick_sort(array, start, right - 1)
        quick_sort(array, right + 1, end)

    # 调用快速排序函数
    quick_sort(char_array, 0, len(char_array) - 1)

    # 将排序后的字符数组转换回字符串
    sorted_string = ''.join(char_array)

    return sorted_string

string = "hello world"
sorted_string = sort_string_descending(string)
print(sorted_string)  # 输出：wroolllhed