在python中实现二进制搜索树？

问题描述

我正在尝试在python中为BST做插入功能，但是我只是对如何正确访问公共方法感到困惑，这给我带来了一些麻烦，现在当我对其进行测试时，它在第一次测试时就停止了，并说nonetype对象没有属性数据，但是当t = tree（）并且tree没有数据构造函数时，我应该如何访问数据？

<div>
  <img src="https://picsum.photos/2000" alt="a random image">
</div>

这是我正在运行的测试用例

class Node(object):
    def __init__(self,data):
       self.parent = None
       self.left = None
       self.right = None
       self.data = data

class Tree(object):
# Binary Search Tree
# class constants
PREORDER = 1
INORDER = 2
POSTORDER = 3

   def __init__(self):
    # Do not create any other private variables.
    # You may create more helper methods as needed.
       self.root = None

   def print(self):
    # Print the data of all nodes in order
      self.__print(self.root)


   def __print(self,curr_node):
    # Recursively print a subtree (in order),rooted at curr_node
       if curr_node is not None:
           self.__print(curr_node.left)
           print(str(curr_node.data),end=' ')  # save space
           self.__print(curr_node.right)


   def insert(self,data):
    # Find the right spot in the tree for the new node
    # Make sure to check if anything is in the tree
    # Hint: if a node n is null,calling n.getData() will cause an error
      root = Node(data)
      print("this is my",self.root)
      if self.root is None:
          self.root = root
          return Node(data)
      else:
          if root.data == data:
              return root
          elif root.data < data:
              root.right = insert(root.right,data)
          else:
              root.left = insert(root.left,data)
      return root

解决方法

提供了两个选项

1. 为插入到树中添加了一个辅助函数（类似于辅助打印函数__print）。这样可以跟踪我们正在树中遍历的节点
2. 通过节点处理的非递归插入。

两个选项均满足单元测试。

选项1-添加要插入的实用程序功能

文件labe3.py

class Node(object):
    def __init__(self,data):
        self.parent = None
        self.left = None
        self.right = None
        self.data = data

class Tree(object):
    # Binary Search Tree
    # class constants
    PREORDER = 1
    INORDER = 2
    POSTORDER = 3

    def __init__(self):
        # Do not create any other private variables.
        # You may create more helper methods as needed.
        self.root = None

    def print(self):
        # Print the data of all nodes in order
        self.__print(self.root)

    def __print(self,curr_node):
        # Recursively print a subtree (in order),rooted at curr_node
        if curr_node is not None:
            self.__print(curr_node.left)
            print(str(curr_node.data),end=' ')  # save space
            self.__print(curr_node.right)

    def insert(self,d):
        print("this is my",self.root)
        if self.root is None:
          self.root = Node(d)
        else:
          self._insert(self.root,d) # here's the call to a "private" function to which we are passing nodes down,starting from root

    def _insert(self,node,value):
        ''' helper function for insert 
               node - node in BST to add value
               value - value to add
        '''
        if value < node.data:  # we know that `node` cannot be None 
                               # so it's safe to check its value! 
              if node.left:
                self._insert(node.left,value) # the recursive call is done only when `node.left` is not None
              else:
                node.left = Node(value)  # direct assignment
        else:
            if node.right:
                self._insert(node.right,value)
            else:
                node.right = Node(value)  # direct assignment
        

选项2-非递归插入函数

文件labe3.py

class Node(object):
    def __init__(self,self.root)
        if self.root is None:
          self.root = Node(d)
        else:
          # current node
          current = self.root

          # Finds node to add data
          while True:
              if current.data > d:
                  if current.left == None:
                      current.left = Node(d)
                      break
                  else:
                      current = current.left

              elif current.data < d:
                  if current.right == None:
                      current.right = Node(d)
                      break
                  else:
                      current = current.right

              else:  
                break
       

文件main.py

import lab3
import unittest

class T0_tree__insert(unittest.TestCase):

    def test_balanced_binary_search_tree(self):
        print("\n")
        print("tree_insert_with_individual_check")
        t = lab3.Tree()

        t.insert(4)
        t.insert(2)
        t.insert(6)
        t.insert(1)
        t.insert(3)
        t.insert(5)
        t.insert(7)

        #The following check is without using tree as an iterator (which uses inorder traversal)
        #So this function also does not check the implementation of the traversal function

        self.assertEqual(t.root.data,4)
        self.assertEqual(t.root.left.data,2)
        self.assertEqual(t.root.left.left.data,1)
        self.assertEqual(t.root.left.right.data,3)
        self.assertEqual(t.root.right.data,6)
        self.assertEqual(t.root.right.left.data,5)
        self.assertEqual(t.root.right.right.data,7)

        print("\n")
        
if __name__ == '__main__':
    unittest.main()

输出

tree_insert_with_individual_check
this is my None
this is my <lab3.Node object at 0x7fa4386b92e0>
this is my <lab3.Node object at 0x7fa4386b92e0>
this is my <lab3.Node object at 0x7fa4386b92e0>
this is my <lab3.Node object at 0x7fa4386b92e0>
this is my <lab3.Node object at 0x7fa4386b92e0>
this is my <lab3.Node object at 0x7fa4386b92e0>


.
----------------------------------------------------------------------
Ran 1 test in 0.001s

OK