0104_maximum_depth_of_binary_tree.cpp

/*
* Copyright(c) 2019 Jiau Zhang
* For more information see <https://github.com/JiauZhang/algorithms>
* 
* This repo is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation
*
* It is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with THIS repo. If not, see <http://www.gnu.org/licenses/>.
*/

/*
* https://leetcode-cn.com/problems/maximum-depth-of-binary-tree
* 题目描述：
*     给定一个二叉树，找出其最大深度。
*     二叉树的深度为根节点到最远叶子节点的最长路径上的节点数。
* 
* 说明: 
*     叶子节点是指没有子节点的节点。
* 
* 示例：
*     给定二叉树 [3,9,20,null,null,15,7]，
* 
*         3
*        / \
*       9  20
*         /  \
*        15   7
*     返回它的最大深度 3 。
*/

/**
 * 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;
        
        int left = maxDepth(root->left);
        int right = maxDepth(root->right);

        return max(left, right) + 1;
    }
};