字符流中第一个不重复的字符

class Solution
{
private:
    string str;
    int num[256]={0};
    
public:
  //Insert one char from stringstream
    void Insert(char ch)
    {
        
         str=str+ch;//将字符ch添加到字符串
         num[ch]++;//利用哈希表存储字符出现次数
    }
  //return the first appearence once char in current stringstream
    char FirstAppearingOnce()
    {
        int len=str.size();
        for(int i=0;i<len;i++){
            if(num[str[i]]==1)
                return str[i];
            
        }
       return '#';
    }

};