# 二叉树的最小深度

<p>给定一个二叉树，找出其最小深度。</p>

<p>最小深度是从根节点到最近叶子节点的最短路径上的节点数量。</p>

<p><strong>说明：</strong>叶子节点是指没有子节点的节点。</p>

<p> </p>

<p><strong>示例 1：</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2020/10/12/ex_depth.jpg" style="width: 432px; height: 302px;" />
<pre>
<strong>输入：</strong>root = [3,9,20,null,null,15,7]
<strong>输出：</strong>2
</pre>

<p><strong>示例 2：</strong></p>

<pre>
<strong>输入：</strong>root = [2,null,3,null,4,null,5,null,6]
<strong>输出：</strong>5
</pre>

<p> </p>

<p><strong>提示：</strong></p>

<ul>
	<li>树中节点数的范围在 <code>[0, 10<sup>5</sup>]</code> 内</li>
	<li><code>-1000 <= Node.val <= 1000</code></li>
</ul>


## template

```java
class TreeNode {
	int val;
	TreeNode left;
	TreeNode right;

	TreeNode(int x) {
		val = x;
	}
}

class Solution {
	public int minDepth(TreeNode root) {

		if (root == null) {
			return 0;
		}

		if (root.left == null && root.right == null) {
			return 1;
		}

		int min_depth = Integer.MAX_VALUE;
		if (root.left != null) {
			int countLeft = 1;
			countLeft += minDepth(root.left);
			min_depth = Math.min(countLeft, min_depth);
		}
		if (root.right != null) {
			int countRight = 1;
			countRight += minDepth(root.right);
			min_depth = Math.min(min_depth, countRight);
		}
		return min_depth;
	}
}

```

## 答案

```java

```

## 选项

### A

```java

```

### B

```java

```

### C

```java

```