// Textbook fragment 06.19
/** List of favorite elements, with their access counts. */
public class FavoriteList<E> {
  protected PositionList<Entry<E>> fList;       // List of entries
  /** Constructor; O(1) time */
  public FavoriteList() { fList = new NodePositionList<Entry<E>>(); }
  /** Returns the number of elements in the list; O(1) time */
  public int size() { return fList.size(); }
  /** Returns whehter the list is empty; O(1) time */
  public boolean isEmpty() { return fList.isEmpty(); }
  /** Removes a given element, provided it is in the list; O(n) time */
  public void remove(E obj) {
    Position<Entry<E>> p = find(obj);   // search for obj
    if (p != null)
      fList.remove(p);          // remove the entry
    }
  /** Increments the access count for the given element and inserts it
    * if it is not already present; O(n) time */
  public void access(E obj) {
    Position<Entry<E>> p = find(obj);   // find the position of obj
    if (p != null)
      p.element().incrementCount();     // increment access count
    else {
      fList.addLast(new Entry<E>(obj)); // add the new entry at the end
      p = fList.last();
    }
    moveUp(p);          // moves the entry to its final position
    }
  /** Finds the position of a given element, or returns null; O(n) time */
  protected Position<Entry<E>> find(E obj) {
    for (Position<Entry<E>> p: fList.positions())
      if (value(p).equals(obj))
        return p;       // fount at position p
    return null;        // not found
  }
  /** Moves up an entry to its correct position in the list;  O(n) time */
  protected void moveUp(Position<Entry<E>> cur) {
    Entry<E> e = cur.element();
    int c = count(cur);
    while (cur != fList.first()) {
      Position<Entry<E>> prev = fList.prev(cur);        // previous position
      if (c <=  count(prev)) break;     // entry is at correct position
      fList.set(cur, prev.element());   // move down previous entry
      cur = prev;
    }
    fList.set(cur, e);  // store the entry in its final position
  }