54.字符流中第一个不重复的字符

public class Solution {
    int[] hashtable=new int[256];
    StringBuilder s=new StringBuilder();
    //Insert one char from stringstream
    public void Insert(char ch){
        s.append(ch);
        if(hashtable[ch]==0){
            hashtable[ch]=1;
        }else{
            hashtable[ch]+=1;
        }
    }
  //return the first appearence once char in current stringstream
    public char FirstAppearingOnce(){
        char[] str=s.toString().toCharArray();
        for(char c:str){
            if(hashtable[c]==1){
                return c;
            }
        }
        return ‘#‘;
    }
}