我的二进制搜索树方法插入有什么问题？

Question

from random import randint


class Node:
    def __init__(self, value=None, left_child=None, right_child=None):
        self.value = value
        self.left_child = left_child
        self.right_child = right_child


class BinarySearchTree:

    def __init__(self):
        self.root = Node()

    def __str__(self):
        return 'bst'

    def insert(self, root, value):
        if root.value is None:
            node = Node(value)
            root = node
        else:
            if value < root.value:
                self.insert(root.left_child, value)
            else:
                self.insert(root.right_child, value)

bst = BinarySearchTree()
data = []
for i in range(100):
    data.append(randint(0,100))
    bst.insert(bst.root, data[i])
print(bst.root.value)

I insert some nodes to the binary search tree, but all nodes of binary tree are still None. Are there anyone who can help me figure this out? Thanks.

Answer 1

Saying root = node is just making root reference something else. The object that was passed in is just no longer being referenced by root . It does not change the object that was passed in. Instead, say for k,v in vars(node).items(): setattr(root, k, v)

Answer 2

You are mixing up your references.

If you instantiate your BST, you make its root a Node() . Absolutely right. When inserting, you check for the value of this node (in the first step). Still okay. Then, you assign a new instance of Node to a local variable, which you will not be able to access afterwards.

In addition, your logic of creating new Node s is improper. You must check for root itself to be None before testing its value. Otherwise, you'll never make children ;_;

Here's your fix:

class Node:
    def __init__(self, value=None, left_child=None, right_child=None):
        self.value = value
        self.left_child = left_child
        self.right_child = right_child


class BinarySearchTree:
    def __init__(self):
        self.root = Node()

    def __str__(self):
        return 'bst'

    def insert(self, root, value):
        if root is None:
            root = Node()
        if root.value is None:
            root.value = value
        else:
            if value < root.value:
                self.insert(root.left_child, value)
            else:
                self.insert(root.right_child, value)

if __name__ == '__main__':
    bst = BinarySearchTree()
    data = []
    for i in range(100):
        data.append(randint(0,100))
        bst.insert(bst.root, data[i])
    print(bst.root.value)