思路：
1，遍历字符串中的字符，求出count数存入字典中
2，求出字典中value值最小的key值存入list
3，遍历字符串，输出不在2中list中字符
#! /usr/bin/python
import string
def del_less_str(new_str):
num_dec={}
for i in new_str:
num=0
for j in new_str:
if i is j:
num=num+1
num_dec[i]=num
a_list=[v for v in num_dec.values()]
b_list=[key for key,value in num_dec.items() if value == min(a_list)]
res=''
for i in new_str:
if i in b_list:
pass
else:
res+=i
return res
if __name__=="__main__":
new_str='aabacja121dkjc'
print(new_str)
str_dic=del_less_str(new_str)
print(str_dic)
