python 3 时间复杂度O(1)解法

from collections import OrderedDict

class Solution:
# 返回对应char
def init(self):
# 初始化一个有序字典(里边的键全是只出现一次的)
self.doulist = []
self.array = OrderedDict()

def FirstAppearingOnce(self):
    # write code here
    if self.array:
        for i in self.array:
            return i
    return '#'

def Insert(self, char):
    # write code here
    # 如果新字符已经存在字典中，就把字典中的该字符删掉
    if char in self.array:
        del self.array[char]
    else:
        # 如果新字符不存在与字典中，则添加到字典中
        if char in self.doulist:
            pass
        else:
            self.doulist.append(char)
            self.array[char] = char