剑指Offer54：字符流中第一个不重复的字符

思路：

 char 是一个个的字符。s是所有char合起来的字符串。Insert函数统计每个字符出现的个数。FirstAppearingOnce函数找出第一个不重复字符。

# -*- coding:utf-8 -*-
class Solution:
    # 返回对应char
    def __init__(self):
        self.s = ''
        self.dict = {}
    def FirstAppearingOnce(self):
        # write code here
        for i in self.s:
            if self.dict[i] == 1:
                return i
        return '#'
    def Insert(self, char):
        # write code here
        self.s += char
        if char in self.dict:
            self.dict[char] += 1
        else:
            self.dict[char] = 1