LeetCode-in-All

104. Maximum Depth of Binary Tree

Easy

Given the root of a binary tree, return its maximum depth.

A binary tree’s maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

Example 1:

Input: root = [3,9,20,null,null,15,7]

Output: 3

Example 2:

Input: root = [1,null,2]

Output: 2

Example 3:

Input: root = []

Output: 0

Example 4:

Input: root = [0]

Output: 1

Constraints:

Solution

#include <algorithm>

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    int maxDepth(TreeNode* root) {
        return findDepth(root);
    }

private:
    int findDepth(TreeNode* node) {
        if (node == nullptr) {
            return 0;
        }
        return 1 + std::max(findDepth(node->left), findDepth(node->right));
    }
};