# 【LeetCode】 104. Maximum Depth of Binary Tree

## Description
> 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.

> 給一棵二元樹，找到它最大深度。

> 最大深度代表從樹根到最遠樹葉的距離。

> 提示：樹葉指一個沒有小孩的節點。

## Example:

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

    3
   / \
  9  20
    /  \
   15   7
return its depth = 3.

## Solution

* 用一個變數代表最深深度，一個變數代表現在深度，跑DFS即可。

### Code

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    void FindDepth(TreeNode* node, int nowdepth,int &depth)
    {
        if(!node)return;
        depth = max(depth,nowdepth);
        FindDepth(node->left,nowdepth+1,depth);
        FindDepth(node->right,nowdepth+1,depth);
    }
    
    int maxDepth(TreeNode* root) {
        int depth=0;
        FindDepth(root,1,depth);
        return depth;
    }
};

###### tags: `LeetCode` `C++`