Introduction to Programming in Python, Aug-Dec 2011
                          Assignment 9
                  Due Saturday, 26 November, 2011

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NOTE: The usual rules apply about file names for submitting your
      assignment.
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Filename: bstree.py

Update the Python class for search trees 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. To compute the slope efficiently,
you have to also maintain and update height information at each
node.

The Python class should be called BSTree.

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