How to make elements of vector unique? (remove non adjacent duplicates)

Question

I have a vector containing few non-adjacent duplicates.

As a simple example, consider:

2 1 6 1 4 6 2 1 1

I am trying to make this

Answer 1

You can remove some of the loops in fa's answer using remove_copy_if:

class NotSeen : public std::unary_function 
{
public:
  NotSeen (std::set & seen) : m_seen (seen) { }

  bool operator ()(int i) const  {
    return (m_seen.insert (i).second);
  }

private:
  std::set & m_seen;
};

void removeDups (std::vector const & iv, std::vector & ov) {
  std::set seen;
  std::remove_copy_if (iv.begin ()
      , iv.end ()
      , std::back_inserter (ov)
      , NotSeen (seen));
}

This has no affect on the complexity of the algorithm (ie. as written it's also O(n log n)). You can improve upon this using unordered_set, or if the range of your values is small enough you could simply use an array or a bitarray.