#include <iostream>
#include <vector>
#include <algorithm>
#include <iterator>
using namespace std;
 
template<typename T>
typename vector<T>::iterator FindFirstDuplicate( vector<T>& v, typename vector<T>::iterator& dupe )
{
	auto current = v.begin();
 
	while (
		current != v.end() &&
		(dupe = std::find( std::next( current ), v.end(), *current )) == v.end()
	)
	{
		++current;
	}
 
	return current;
}
 
int main() {
 
	vector<int> v = { 1,2,3,4,5,6,5,4,3 };
	auto dupe = v.begin();
	auto it = FindFirstDuplicate(v,dupe);
	cout << "first dupe is " << *it << " at pos " << it - v.cbegin() << endl;
	cout << "dupe is " << *dupe << " at pos " << dupe - v.cbegin() << endl;
 
	std::rotate( v.begin(), it, v.end() )	;
	return 0;
}

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