# CSE 522 Assignment 1: Code Reuse in BSTs solved

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## Description

In the class lectures, we discussed two object-oriented definitions of the binary search tree (BST),
called class Tree and class AbsTree respectively. In this assignment, you are to complete the
definition of a delete operation for both versions of the binary search tree. Part1 pertains to
defining delete for Tree and Part2 pertains to defining delete is for AbsTree.
Part 1: Define delete in class Tree
Preliminaries: Refer to BST_Part1.java posted at Resources  Homeworks. It provides
the starting point for Part 1.
A protected field Tree parent field has been added to class Tree. Revise the insert method so
that the parent field is correctly set when a value is inserted into the tree. Define three
procedures, min(), max(), and find(n) which return, respectively, the Tree node with the
minimum value, the Tree node with the maximum value, and the Tree node containing the value
n. If n is not present in the tree, find(n) should return null.
Defining delete: The delete(n) method should remove value n from the tree if it is present in
the tree while ensuring that the remaining values maintain the binary search tree property. A
good explanation of delete is given at:
http://www.algolist.net/Data_structures/Binary_search_tree/Removal
There are four main cases to delete depending upon whether the value to be deleted is at:
(i) A leaf node (but not the root); or
(ii) A non-leaf node (not the root) with only one non-null subtree; or
(iii) A root node with one non-null subtree; or
(iv) A node with both non-null subtrees.
Note that we do not allow the root node to be deleted if it has both null subtrees.
The top-level definition of the delete(n) method in class Tree has been provided to you – do not
modify this definition. The method makes use of four helper methods, called case1, case2,
case3L, and case3R. The methods case1 and case2 correspond to cases (i) and (ii) above while
case (iii) is implemented using two methods, called case3L and case3R, depending upon whether
the missing tree is on the left (case3R) or the right (case3L). Case (iv) can be handled using
case3L or case3R.
The file BST_Part1.java provides the outline of class Tree and the definition of the driver class,
BST_Part1, which contains method main. Your task is to provide definitions of the four helper
methods for delete in addition to the methods min, max, and find.
A screen-cast BST_Part1.mp4 will be posted clarifying the cases of delete.
Run your program under JIVE and save the object and sequence diagrams in files called obj.png
and seq.png, respectively, at the point when all insert and delete operations have been
performed by main, but main has not yet exited. For the object diagram, choose the ‘Stacked
with Tables’ option.
Note: Print out error messages on the Console when the value to be deleted is either not present
in the tree or is present at the root of the tree with both subtrees null.
What to Submit: Prepare a top-level directory named A1_Part1_UBITId1_UBITId2 if the
assignment is done by two students (list the UBITIds in alphabetic order); otherwise, name it as
A1_Part1_UBITId if the assignment is done solo.
In this directory, place BST_Part1.java, obj.png and seq.png. Compress the directory
and submit the compressed file using the Linux command submit_cse522. Details regarding
online submission will be posted in due course at
Resources  Homeworks  Online_Submission_CSE522.pdf
Only one submission per team is required.
End of Part 1
Part 2: Define delete in class AbsTree
Will be posted soon.