Map-e.g.

/***User register using name, if not exist in DB, add to db and return ok, 
if already exist new user name to be created using rule least i is appended and prompted back to user
#user i/p will be n (number of registration requests) and o/p will be ok/newname***/

#include <iostream>
#include <vector>
#include <map>
#include <sstream>
using namespace std;

vector<string> vDB;
map<string, int> nameFrequency;

string processRegistrationRequest(string name)
{
    if(nameFrequency[name] == 0)
    {
        vDB.push_back(name);
        nameFrequency[name]++;       
        return "ok";
    }
    else
    {
        
        stringstream str;
        str<<name<<nameFrequency[name];
        
        vDB.push_back(str.str());
        nameFrequency[name]++;
        return str.str();
    }
}

int main() {
    
    int numberOfRequests = 0;
    cin >> numberOfRequests;
    
    string name;
    
    for(int i=0; i<numberOfRequests; i++)
    {
        cin >> name;
        cout<< processRegistrationRequest(name) <<endl;
    }
    
    cout<<"DB"<<endl;
    
    for(auto x: vDB)
        cout<<x<<endl;
    
    return 0;
}