DFS:104. Maximum Depth of Binary Tree

最大深度，典型的dfs。差点又想加一个if(root->left == NULL && root->right == NULL)，没必要。代码很简单：

/** * 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:    int maxDepth(TreeNode* root) {        if(root == NULL )            return 0;        else            return max(maxDepth(root->left), maxDepth(root->right)) + 1;    }};