# 二叉树的最大深度

<p>给定一个二叉树，找出其最大深度。</p>

<p>二叉树的深度为根节点到最远叶子节点的最长路径上的节点数。</p>

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

<p><strong>示例：</strong><br>
给定二叉树 <code>[3,9,20,null,null,15,7]</code>，</p>

<pre>    3
   / \
  9  20
    /  \
   15   7</pre>

<p>返回它的最大深度&nbsp;3 。</p>


## template

```java

public class TreeNode {
	int val;
	TreeNode left;
	TreeNode right;

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

class Solution {
	public int maxDepth(TreeNode root) {

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

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

		int leftDeep = 0;
		if (root.left != null) {

			leftDeep = 1 + maxDepth(root.left);
		}

		int rightDeep = 0;
		if (root.right != null) {
			rightDeep = 1 + maxDepth(root.right);
		}

		return deep + leftDeep > rightDeep ? leftDeep : rightDeep;
	}
}

```

## 答案

```java

```

## 选项

### A

```java

```

### B

```java

```

### C

```java

```