字符集合

#include<iostream>
#include<string>
#include<unordered_set>
using namespace std;
int main()
{
    string str;
    while(cin>>str)
    {
        unordered_set<char>record;
        string res;
        for(int i=0;i<str.size();i++)
        {
            if(record.count(str[i])==false)
            {
                res+=str[i];
                record.insert(str[i]); 
            }
        }
        cout<<res<<endl;
    }
}