从列表列表中选择重复的列表(Python 2.7.13)

def find_duplicates(lst):
    duplicates = set()
    unique_elements = set()

    for element in lst:
        if element in unique_elements:
            duplicates.add(element)
        else:
            unique_elements.add(element)

    return duplicates

# 示例用法
my_list = [1, 2, 3, 4, 5, 2, 3, 6, 7, 8, 9, 1]
result = find_duplicates(my_list)
print(result)

{1, 2, 3}