0701._Insert_into_a_Binary_Search_Tree.md

# 701. Insert into a Binary Search Tree 

**<font color=red>难度: Hard</font>**

## 刷题内容

> 原题连接

* https://leetcode.com/problems/longest-valid-parentheses

> 内容描述

```
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:

         4
       /   \
      2     7
     / \   /
    1   3 5
This tree is also valid:

         5
       /   \
      2     7
     / \   
    1   3
         \
          4
```

## 解题方案

> 思路 1

就一句话，看到树🌲就想到递归，太简单了，30秒敲完答案

```python
class Solution(object):
    def insertIntoBST(self, root, val):
        """
        :type root: TreeNode
        :type val: int
        :rtype: TreeNode
        """
        if not root:
            return TreeNode(val)
        if val < root.val:
            root.left = self.insertIntoBST(root.left, val)
        if val > root.val:
            root.right = self.insertIntoBST(root.right, val)
        return root
```