#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
using namespace std;
 
int main() {
	vector<string> elements{"a","a","b","b","c"};
    // "elements" is populated ....
    //  ...
 
    // Find duplicates:
    vector<string> uniqueElements;
 
    for (int i = 0; i < elements.size(); ++i)
    {
        string name = elements[i];
        vector<string>::iterator it = find(uniqueElements.begin(), uniqueElements.end(), name);
 
        if(it != uniqueElements.end()) // ERROR
        {
            cerr << "Duplicate element " << name << endl;
        }
        else
            uniqueElements.push_back(name);
    }
    for (const auto & e : uniqueElements)
        std::cout << e << std::endl;
	return 0;
}

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