def permutation(li: list, level: int):
    """
    :param li: 排列对象转列表
    :param level: 排列起点
    :return:
    """
    if level == len(li):
        print(li)
    for i in range(level, len(li)):
        li[level], li[i] = li[i], li[level]
        permutation(li, level + 1)
        li[level], li[i] = li[i], li[level]