[LeetCode] 104. Maximum Depth of Binary Tree

题目链接：传送门

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.

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

    3

   / \

  9  20

    /  \

   15   7

return its depth = 3.

Solution

题意：

求一棵二叉树的最大深度

思路：

dfs

/**
 * 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 dfs(TreeNode* root, int depth, int &res) {
        if (!root)  return ;
        res = max(res, depth);
        dfs(root->left, depth + 1, res);
        dfs(root->right, depth + 1, res);
    }
    int maxDepth(TreeNode* root) {
        if (!root)  return 0;
        int res = 0;
        dfs(root, 1, res);
        return res;
    }
};