104. Maximum Depth of Binary Tree

1. 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.

2. Note

• A leaf is a node with no children.

3. Example

Example 1:
Given binary tree [3,9,20,null,null,15,7],
return its depth = 3.

4. Constraints

• The number of nodes in the tree is in the range [0, $10^4$].
• -100 <= Node.val <= 100

4. Solutions

Recursive

n is the number of nodes in i_root
Time complexity: O(n)
Space complexity: O(n)

class Solution {
public:
    int maxDepth(TreeNode* root) {
        if (root == nullptr) {
            return 0;
        } else {
            return 1 + max(maxDepth(root->left), maxDepth(root->right));
        }
    }
};