code: private void moveAtFirst(int n_from) {
  		int eT = elements[0];
  		int eF = elements[n_from];
  		positions[eT] = -1;
  		positions[eF] = 0;
  		elements[0] = eF;
  		elements[n_from] = -1;
  	}
docs: moveAtFirst data in node n_from to node 0
  Erase previous information of node 0
  
  @param n_from index of the node of the source data