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# 0742. Closest Leaf in a Binary Tree

<https://leetcode.com/problems/closest-leaf-in-a-binary-tree>

## Description

Given the `root` of a binary tree where every node has **a unique value** and a target integer `k`, return *the value of the **nearest leaf node** to the target* `k` *in the tree*.

**Nearest to a leaf** means the least number of edges traveled on the binary tree to reach any leaf of the tree. Also, a node is called a leaf if it has no children.

**Example 1:**

![](https://assets.leetcode.com/uploads/2021/06/13/closest1-tree.jpg)

```
**Input:** root = [1,3,2], k = 1
**Output:** 2
**Explanation:** Either 2 or 3 is the nearest leaf node to the target of 1.
```

**Example 2:**

![](https://assets.leetcode.com/uploads/2021/06/13/closest2-tree.jpg)

```
**Input:** root = [1], k = 1
**Output:** 1
**Explanation:** The nearest leaf node is the root node itself.
```

**Example 3:**

![](https://assets.leetcode.com/uploads/2021/06/13/closest3-tree.jpg)

```
**Input:** root = [1,2,3,4,null,null,null,5,null,6], k = 2
**Output:** 3
**Explanation:** The leaf node with value 3 (and not the leaf node with value 6) is nearest to the node with value 2.
```

**Constraints:**

* The number of nodes in the tree is in the range `[1, 1000]`.
* `1 <= Node.val <= 1000`
* All the values of the tree are **unique**.
* There exist some node in the tree where `Node.val == k`.

## ac

```java
```