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)