import DAT.*;

public class BintreeLinked {

  TreeCell beforeRoot;

  // constructor

  public BintreeLinked () {beforeRoot = new TreeCell(null, null, null);}


  // checkers

  public boolean isEmpty() {return beforeRoot.children[0] == null;}

  public boolean isExternal(TreeWindow w) {
    return w.parentnode.children[w.childnum] == null;
  }
  
  public boolean isLeaf(TreeWindow w) {
    return !isExternal(w) 
      && w.parentnode.children[w.childnum].children[0] == null
      && w.parentnode.children[w.childnum].children[1] == null;
  }


  // manipulators

  public void initialise(TreeWindow w) {
    w.parentnode = beforeRoot;
    w.childnum = 0;
  }


}