#!/usr/bin/env python
#!-*-coding:utf-8 -*-
def run(lit):
# 判断lit中是否有重复的元素
if [lit.count(x) for x in lit if lit.count(x) > 1]:
lit1 = []
for i in lit:
if lit.count(i) > 1:
lit1.append(i)
# 将lit2去重并保持原顺序
lit2 = list(set(lit1))
lit2.sort(key=lit1.index)
# lit中有重复的元素,则返回重复的元素列表lit2
return lit2
# lit中没有重复的元素,则返回None
return None
print(run([1, 2, 3, 4, 5, 6, 7, 8, 9, 3, 4, 8, 0]))