# LeetCode: 701. Insert into a Binary Search Tree

## 题目¶

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
```

Constraints:

• The number of nodes in the given tree will be between 0 and 10^4.
• Each node will have a unique integer value from 0 to -10^8, inclusive.
• -10^8 <= val <= 10^8
• It's guaranteed that val does not exist in the original BST.

## 解法¶

### 利用 BST 特性进行节点插入¶

1. 如果要插入的值小于当前节点的值，说明需要把它插入到左侧的子节点中。
2. 如果要插入的值大于当前节点的值，说明需要把它插入到右侧的子节点中。

```# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution(object):
def insertIntoBST(self, root, val):
if root is None:
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
```