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# Problem 270: Closest Binary Search Tree Value

> <https://leetcode.com/problems/closest-binary-search-tree-value/#/description>

![](https://1241747088-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-Lpv9LvBSlFaukf_ALqh%2F-Lpv9NPw3Ji1X5Vk8CES%2F-Lpv9vw1P9wQdC20v2g5%2F270.png?generation=1569729533116865\&alt=media)

## 思路

* 这道题在 Google 面试的时候遇到了，当时竟然懵逼了。主要是当时没有注意是 Binary Search Tree，也就是隐含了一个信息是：

所有的元素是从左到右排列好的。

* 用个一个元素标记最接近的值，然后遇到更接近的就更新。
* root 走的方向通过最接近的路径走。

```java
/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int closestValue(TreeNode root, double target) {
        int closest = root.val;
        while (root != null) {
            if (Math.abs(root.val - target) < Math.abs(closest - target)) closest = root.val;

            root = (root.val > target ? root.left : root.right);
        }

        return closest;
    }
}
```