Maximum Depth of Binary Tree

Problem

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

Constraints:

The number of nodes in the tree is in the range [0, 104].
-100 <= Node.val <= 100

Solution

• left/right 노드로 계속 진입하고, 리턴하는 값 중에 더 큰 것을 받아와 +1을 해준다
• Time compexity : O(n)
• Space compexity : O(height of trees)

Code

//https://leetcode.com/problems/maximum-depth-of-binary-tree/
/**
 * 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)
    {
        if (root == nullptr) return 0;

        int l = maxDepth(root->left);
        int r = maxDepth(root->right);
        return max(l, r) + 1;
    }
};