[leetcode] 701. Insert into a Binary Search Tree @ python

二叉搜索树插入操作

最新推荐文章于 2023-02-25 22:41:55 发布

原创最新推荐文章于 2023-02-25 22:41:55 发布 · 261 阅读

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本文详细解析了如何在二叉搜索树中插入一个新值，通过递归方法确保树的性质不变。提供了Python实现代码，展示了不同可能的插入结果。

原题

Given the root node of a binary search tree (BST) and a value to be inserted into the tree, insert the value into the BST. Return the root node of the BST after the insertion. It is guaranteed that the new value does not exist in the original BST.

Note that there may exist multiple valid ways for the insertion, as long as the tree remains a BST after insertion. You can return any of them.

For example,

Given the tree:
4
/
2 7
/
1 3
And the value to insert: 5
You can return this binary search tree:

This tree is also valid:

解法

递归. Base case是当根节点为空时, 返回单独节点TreeNode(val), 如果根节点是叶子节点, 那么插入val节点作为根节点的左子树或右子树. 然后往下递归.
Time: O(h) h为二叉树的高度
Space: O(1)

代码

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def insertIntoBST(self, root, val):
        """
        :type root: TreeNode
        :type val: int
        :rtype: TreeNode
        """
        # base case
        if not root:
            return TreeNode(val)
        if root.left is None and root.right is None:
            if root.val > val:
                root.left = TreeNode(val)
            else:
                root.right = TreeNode(val)
            return root
        if root.val > val:
            root.left =  self.insertIntoBST(root.left, val)
        else:
            root.right =  self.insertIntoBST(root.right, val)
        return root