104. Maximum Depth of Binary Tree

题目：Maximum Depth of Binary Tree

原题链接
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.
找出二叉树的最大深度

找深度的话只能不断的遍历下去了，深度优先和广度优先遍历都是可以的，这里就给出深度优先的代码：

/**
 * 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;
        return max(maxDepth(root -> left) + 1,maxDepth(root -> right) + 1);
    }
};