# [104. Maximum Depth of Binary Tree](https://leetcode.com/problems/maximum-depth-of-binary-tree/)

## 题目

Given a binary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

**Note**: A leaf is a node with no children.

**Example**:

Given binary tree [3,9,20,null,null,15,7],

```

    3
   / \
  9  20
    /  \
   15   7

```

return its depth = 3.
 

## 题目大意

要求输出一棵树的最大高度。

## 解题思路

这一题递归遍历就可，遍历根节点的左孩子的高度和根节点右孩子的高度，取出两者的最大值再加一即为总高度。




## 代码

```go

package leetcode

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func maxDepth(root *TreeNode) int {
	if root == nil {
		return 0
	}
	return max(maxDepth(root.Left), maxDepth(root.Right)) + 1
}

```