Asking how to insert a new node to BST? Python

Question

I am doing my practice, and the practice request create DSATreeNode and DSABinarySearchTree classes. The DSATreeNode is working fine, but when I use the function of insertRec. The insert function will call the insertRec that store the node in the right place. The problem comes is it is not storing and there is nothing in new node. Also the self._root is None, never insert anything into it.

Here's my code

class DSATreeNode:
    def __init__(self, inKey, inValue):
        self._key = inKey
        self._value = inValue
        self._left = self._right = None

class DSABinarySearchTree:
    def __init__(self):
        self._root = None

    def find(self, key):
        return self._findRec(key, self._root)
    
    def _findRec(self, key, cur):
        value = None
        if cur == None: # Base case: not found
            raise Exception("Key " + key + " not found")
        elif key == cur._key: # Base case: found
            value = cur._value
        elif key < cur._key: # Go left (recursive)
            value = self._findRec(key, cur._left)
        else: # Go right(recursive)
            value = self._findRec(key, cur._right)
        
        return value

    def insert(self, inKey, inValue):
        return self.insertRec(inKey, inValue, self._root)

    def insertRec(self, key, value, curNode):
        createNode = DSATreeNode(key, value)
        if curNode == None:
            curNode = createNode
        elif key < curNode._key:
            curNode._left = self.insertRec(key, value, curNode._left)
        else:
            curNode._right = self.insertRec(key, value, curNode._right)

    def getRoot(self):
        return self._root._key, self._root._value

You do not return curNode in recursion, and it is unnecessary to create a new node every time you recurse. — Mechanic Pig
– Mechanic Pig, Commented Sep 12, 2022 at 3:37
Yes, and you only need to create a new node when curNode is None. — Mechanic Pig
– Mechanic Pig, Commented Sep 12, 2022 at 3:50
Please don't spam tags. This has nothing to do with digital signature algorithm (DSA). — Evg
– Evg, Commented Sep 12, 2022 at 16:12

trincot · Accepted Answer · 2022-09-12 05:26:36Z

0

A few issues:

_insertRec does not return a node. It should have return curNode as its last statement.
There is no code that assigns a node to self._root. The insert method should assign like this: self._root = self.insertRec(inKey, inValue, self._root).
The error message generated in _findRec assumes that key is a string, but if it isn't, then it will fail. Better do raise Exception("Key " + str(key) + " not found") or raise Exception(f"Key {key} not found")
Not blocking, but _insertRec should not create a node when it still is going to make a recursive call. So move that first line into the first if block:
```
    if curNode == None:
        curNode = DSATreeNode(key, value)
```

answered Sep 12, 2022 at 5:26

trincot

357k38 gold badges282 silver badges339 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Asking how to insert a new node to BST? Python

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related