Question

Using Python to solve the question

Problem 5 Binary Search Trees (30 points) Modify the books implementation of the binary search tree described in chapters 6.10-6.13 so that it handles duplicate keys properly. The BinarySearchTree class implements a binary search tree where every node of the tree contains a key and a corresponding data item (the payload). Much like the HashTable class, this is so BinarySearch Tree can be used in a similar manner as a Python dictionary Currently if a key is already in the tree, then a node is added containing duplicate key and its payload. We want this fixed so it behaves like a Python dictionary. If a key is already in the binary search tree then the old payload is replaced with the new payload. No node should be added. The put and_put methods of the BinarySearch Tree class insert nodes into the binary search tree. The put method will check to see if the tree already has a root. If there is not a root then put will create a new node and install it as the root of the tree. If a root node is already in place then put calls the recursive, helper function_put to search the tree for where to insert the new node. The only method you will need to modify is_put. Understand what it is doing before you start proposing changes.

def _put(self,key,val,currentNode):
if key < currentNode.key:
if currentNode.hasLeftChild():
self._put(key,val,currentNode.leftChild)
else:
currentNode.leftChild = TreeNode(key,val,parent=currentNode)
elif key > currentNode.key:
if currentNode.hasRightChild():
self._put(key,val,currentNode.rightChild)
else:
currentNode.rightChild = TreeNode(key,val,parent=currentNode)

Answer 1

Here is the modified code for this method. Assuming the value of a node is stored in an instance variable named val. If it is anything else, update it with that name as needed. (Since you did not provide the complete existing code, I could only guess). Comments are included, go through it, learn how things work and let me know if you have any doubts or if you need anything to change. If you are satisfied with the solution, please rate the answer. Thanks

def _put(self,key,val,currentNode):
    #checking if key is equal to current node's key
    if key == currentNode.key:
        #replacing current node's value to val. Assuming value is stored
        #in instance variable called val. If it is anything different, then
        #replace val with that
        currentNode.val=val
    elif key < currentNode.key:
        if currentNode.hasLeftChild():
            self._put(key,val,currentNode.leftChild)
        else:
            currentNode.leftChild = TreeNode(key,val,parent=currentNode)
    elif key > currentNode.key:
        if currentNode.hasRightChild():
            self._put(key,val,currentNode.rightChild)
        else:
            currentNode.rightChild = TreeNode(key,val,parent=currentNode)