Advanced Programming, Jan-Apr 2012
                          Assignment 3
                        18 February, 2012
                      Due 27 February, 2012
              Deadline extended to 29 February, 2012

The file searchtree.py defines a Python class TNode that implements
search trees with find(), insert() and delete().

1. Update this class to maintain height balance. You have to add
   code for right and left rotations and incorporate a
   rebalancing operation into the insert and delete functions to
   preserve balance. Ensure that slope calculation is efficient.

2. In searchtree.py, __str__() calls a function treeprint() that
   displays the tree rotated 90 degrees to the left. Modify this
   so that __str__() displays the tree in the conventional manner
   with the root on top.

Submit your code in file "bstree.py".  The Python class should be
called BTNode.

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