35.字符流中第一个不重复的字符

题目描述

请实现一个函数用来找出字符流中第一个只出现一次的字符。例如，当从字符流中只读出前两个字符"go"时，第一个只出现一次的字符是"g"。当从该字符流中读出前六个字符“google"时，第一个只出现一次的字符是"l"。 

import java.util.*;public class Solution {    //Insert one char from stringstream    HashMap<Character,Integer> map = new HashMap<Character,Integer>();    ArrayList<Character> list = new ArrayList<Character>();    public void Insert(char ch)    {        if(map.containsKey(ch)){            map.put(ch,map.get(ch)+1);        }else{            map.put(ch,1);        }        list.add(ch);    }  //return the first appearence once char in current stringstream    public char FirstAppearingOnce()    {        Character returnC = '#';    for(Character ch : list){            if(map.get(ch)==1){                returnC = ch;                break;            }        }        return returnC;    }}