题目链接：https://www.nowcoder.com/practice/253986e66d114d378ae8de2e6c4577c1?tpId=37&rp=1&ru=%2Fexam%2Foj%2Fta&qru=%2Fexam%2Foj%2Fta&sourceUrl=%2Fexam%2Foj%2Fta%3Fpage%3D1%26tpId%3D37%26type%3D37&difficulty=&judgeStatus=&tags=&title=&gioEnter=menu
题目如下：

#include 
using namespace std;
int main(){string str="";unordered_set<char> uset;string res="";cin>>str;for(int i=str.size()-1;i>=0;i--){if(uset.count(str[i])==0){res+=str[i];uset.insert(str[i]);}}cout<<res<<endl;return 0;
}