Leetcode NO.104 Maximum Depth of Binary Tree

题目要求如下：

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.

本题应该算是Leetcode里面最简单的题之一了。。

就用单纯的dfs就可以做出，dfs()函数有两个参数，第二个就是储存当前的depth。如果找到了leaf node，此时depth大于之前的max，则替换max。。如果没有找到leaf node，则继续遍历，代码如下：

/** * Definition for binary tree * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    int maxDepth(TreeNode *root) {        count = 0;        if (root == NULL)            return 0;        dfs(root, 0);        return count;    }private:    int count;    void dfs(TreeNode* root, int depth) {        if (root->left == NULL && root->right == NULL) {            if (1 + depth > count)                count = 1 + depth;        }        else {            if (root->left != NULL)                dfs(root->left, depth+1);            if (root->right != NULL)                dfs(root->right, depth+1);        }    }};