#include <iostream>
#include <vector>
 
using namespace std;
 
template <typename T> void duplicate(vector <T> &v)
{
  size_t n = v.size();
  v.resize(n << 1);
 
  for (size_t q=n-1; ~q; --q)
  {
    v[(q<<1)|1] = v[q];
    v[q<<1] = move(v[q]); // should work for 0
  }
}
 
int main(int argc, const char * argv[])
{
  vector<int> v { 1,2,3,4,5,6,7,8,9,10 };
  for(auto i: v) cout << i << "  "; cout << endl;
  duplicate(v);
  for(auto i: v) cout << i << "  "; cout << endl;
}

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