# LeetCode 270. Closest Binary Search Tree Value

## Description

https://leetcode.com/problems/closest-binary-search-tree-value/

Given the `root` of a binary search tree and a `target` value, return the value in the BST that is closest to the `target`.

Example 1:

```Input: root = [4,2,5,1,3], target = 3.714286
Output: 4
```

Example 2:

```Input: root = , target = 4.428571
Output: 1
```

Constraints:

• The number of nodes in the tree is in the range `[1, 104]`.
• `0 <= Node.val <= 109`
• `-109 <= target <= 109`

## Explanation

Base on the characteristics of binary search tree to search for the target.

## Python Solution

``````# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
def closestValue(self, root: TreeNode, target: float) -> int:
self.closest = None

self.search(root, target)

return self.closest.val

def search(self, root, target):
if not root:
return

if not self.closest or abs(root.val - target) < abs(self.closest.val - target):
self.closest = root

if target < root.val:
self.search(root.left, target)
elif target > root.val:
self.search(root.right, target)
``````
• Time Complexity: O(log(N)).
• Space Complexity: O(1).