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#include <iostream>
#include <vector>
#include <algorithm>
#include <iterator>
using namespace std;
 
template<typename T>
typename vector<T>::const_iterator FindFirstDuplicate( const vector<T>& v )
{
	vector<T> nv;
	nv.reserve( v.size() );
	for( auto it1 = v.cbegin(); it1 != v.cend(); ++it1 ) // can be const (?)
	{
		auto it2 = find( nv.cbegin(), nv.cend(), *it1 ); // search elem in new vector
		if( it2 == nv.cend() )                          // if not present,
			nv.push_back( *it1 );                      //  add in new vector
		else                                          // else, means we found a dupe
			return v.begin() + ( it2 - nv.cbegin() );
	}
	return v.begin();
}
 
int main() {
 
	vector<int> v = { 1,2,3,4,5,6,7,8,9,10,3,11 };
	auto it = FindFirstDuplicate(v);
	cout << "first dupe is " << *it << " at " << it - v.cbegin() << endl;
 
	std::rotate( v.begin(), it, v.end() )	;
	return 0;
}

prog.cpp: In function ‘int main()’:
prog.cpp:29:38: error: no matching function for call to ‘rotate(std::vector<int>::iterator, __gnu_cxx::__normal_iterator<const int*, std::vector<int> >&, std::vector<int>::iterator)’
  std::rotate( v.begin(), it, v.end() ) ;
                                      ^
prog.cpp:29:38: note: candidate is:
In file included from /usr/include/c++/4.8/algorithm:62:0,
                 from prog.cpp:3:
/usr/include/c++/4.8/bits/stl_algo.h:1699:5: note: template<class _FIter> void std::rotate(_FIter, _FIter, _FIter)
     rotate(_ForwardIterator __first, _ForwardIterator __middle,
     ^
/usr/include/c++/4.8/bits/stl_algo.h:1699:5: note:   template argument deduction/substitution failed:
prog.cpp:29:38: note:   deduced conflicting types for parameter ‘_FIter’ (‘__gnu_cxx::__normal_iterator<int*, std::vector<int> >’ and ‘__gnu_cxx::__normal_iterator<const int*, std::vector<int> >’)
  std::rotate( v.begin(), it, v.end() ) ;
                                      ^

Standard output is empty