剑指offer 54.字符串 字符流中第一个不重复的字符

            int[] hashtable=new int[256];
            StringBuffer s=new StringBuffer();
            //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 ‘#‘;
            }