'''
题目

输入为两个字符串str1,str2。找出两个字符串中不同的字符
例子

None输入 -> None
'abc','abcc' -> 'c'
'abcd','abcde' -> 'e'
'aaabbcdd','abdbacade' -> 'e'
假设

两个字符串中只有唯一一个字符不同
所有字符均为ascii
tips

统计每个字符出现的次数
利用异或运算
'''

from functools import reduce


def find_diff(s1, s2):
    if s1 is None or s2 is None:
        return None
    list_s2 = list(s2)
    {list_s2.remove(x) for x in s1 if x in s2}
    print(list_s2)
    return ''.join(list_s2)

s1 = 'abc'
s2 = 'abcd'

from collections import Counter
c1 = Counter(s1)
c2 = Counter(s2)
print(c1)
print(c2)
print((c2-c1))
print(''.join(list(c2-c1)))

print('-----------------------------')
# print(reduce(lambda x, y: ord(x) ^ ord(y), s1+s2))
# print(s1+s2)
# 两个字符串中，只有一个唯一字符
def find_diff2(s1, s2):
    s3 = s1 + s2
    i = 1
    temp = ord(s3[0])
    while i < len(s3):
        temp ^= ord(s3[i])
        i += 1
    # print('temp=',chr(temp))
    return chr(temp)

def find_diff3(s1, s2):
    # alist = [ord(x) for x in s1+s2]
    # print(alist)
    return chr(reduce(lambda x, y: x^y, [ord(x) for x in s1+s2]))


print(find_diff3(s1, s2))