Recursive mergeSort to Iterative in c++ using deque

Question

I'm trying to do the iterative version of this multiple recursive mergesort:

I only need to make iterable this sort function:

template<class T> deque<T> mergesort<T>::sort(deque<T> &right){
  int size = right.size();

  if (size <= 1){
    return right;
  }
  int middle = size/2;
  deque<T> left;
  for(int i = 0; i < middle; i++){
    left.push_back(right.front());
    right.pop_front();
  }
  left = sort(left);
  right = sort(right);
  return merge(left, right);
}

The merge function can be the same:

    template<class T> deque<T> mergesort<T>::merge(deque<T> &left, deque<T> &right){
  deque<T> result;

  while(left.size() > 0 || right.size() > 0){

    if (left.size() > 0 && right.size() > 0){

      if (getOrder(left.front(),right.front())){
        result.push_back(left.front());
        left.pop_front();
      }
      else{
        result.push_back(right.front());
        right.pop_front();
      }
    }

    else if(left.size() > 0){
      result.push_back(left.front());
      left.pop_front();
    }
    else if(right.size() > 0){
      result.push_back(right.front());
      right.pop_front();
    }
  }
  return result;
}

It's hard for me to make the tranformation of multiple recursive function to iterative function.

Thanks everyvody and kind regards.

Answer 1

Do you have to use dequeue? The iterative version of merge sort is called a bottom-up merge sort. There's really no need to store extra information.