[剑指offer] 字符流中第一个不重复的字符

import java.util.HashMap;
public class Solution {
    HashMap<Character, Integer> map = new HashMap<Character, Integer>();
    StringBuffer s = new StringBuffer();
    //Insert one char from stringstream
    public void Insert(char ch)
    {
        s.append(ch);
        if(map.containsKey(ch)){
            map.put(ch, map.get(ch)+1);
        }else{
            map.put(ch, 1);
        }
    }
  //return the first appearence once char in current stringstream
    public char FirstAppearingOnce()
    {
        for(int i = 0; i < s.length(); i++){
            if(map.get(s.charAt(i)) == 1)
                return s.charAt(i);
        }
        return '#';
    }
}