没有花里胡哨，言简意赅

没有那么多花里胡哨，言简意赅

class Solution:
    # 返回对应char

    def __init__(self):
        self.char_set = set()
        self.list = []

    def FirstAppearingOnce(self):
        return self.list[0] if len(self.list)>0 else '#'

    def Insert(self, char):
        if char not in self.char_set:
            self.char_set.add(char)
            self.list.append(char)
        else:
            if char in self.list:
                self.list.remove(char)