Question

implement the following functions using recusrion:

1. subst(tnode, t, r). Purpose: To substitute a target value t with a replacement value r wherever it appears as a data value in the given tree. Returns None, but modifies the given tree.

So given a binary tree as tnode, find the target node, t, with and replace it with the replacement, r.

Ex. tnode

1

2 3

4 5

t = 5, r = 10

1

2 3

4 10

Using the follwoing code:

def create(data, left=None, right=None):
    """
    Create a new treenode for the given data.
    Pre-conditions:
        data:  Any data value to be stored in the treenode
        left:  Another treenode (or None, by default)
    Post-condition:
        none
    Return:
        the treenode created
    """
    return {'data':data, 'left':left, 'right':right}


def get_data(treenode):
    """
    Retrieve the contents of the data field.
    Pre-conditions:
        node: a node created by create()
    Post-conditions:
        none
    Return
        the data value stored previously in the node
    """
    return treenode['data']


def get_left(tnode):
    """
    Retrieve the contents of the left field.
    Pre-conditions:
        tnode: a treenode created by create()
    Post-conditions:
        none
    Return
        the value stored in left field
    """
    return tnode['left']


def get_right(tnode):
    """
    Retrieve the contents of the right field.
    Pre-conditions:
        tnode: a treenode created by create()
    Post-conditions:
        none
    Return
        the value stored in right field
    """
    return tnode['right']


def set_data(tnode, val):
    """
    Set the contents of the data field to val.
    Pre-conditions:
        tnode: a node created by create()
        val:  a data value to be stored
    Post-conditions:
        stores the new data value, replacing the existing value
    Return
        none
    """
    tnode['data'] = val


def set_left(tnode, val):
    """
    Set the contents of left field to val.
    Pre-conditions:
        tnode: a treenode created by create()
        val:   a treenode, or the value None
    Post-conditions:
        stores the val in left field, replacing the existing value
    Return
        none
    """
    tnode['left'] = val

def set_right(tnode, val):
    """
    Set the contents of right field to val.
    Pre-conditions:
        tnode: a treenode created by create()
        val:   a treenode, or the value None
    Post-conditions:
        stores the val in right field, replacing the existing value
    Return
        none
    """
    tnode['right'] = val

Answer 1

def subst(tnode,t,r):
if tnode is None:
return None
if tnode['data']==t:
tnode['data']=r#if tnode's data is same as target value then replace
subst(tnode['left'],t,r)#calling function on left subtree
subst(tnode['right'],t,r)#calling function on right subtree