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104. Maximum Depth of Binary Tree

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

SOL：

參考李根逸博士影片的後半段，樹的問題通常用 遞迴關係 + 邊界條件 來解決。

【C 語言的 LeetCode 30 天挑戰】第十一天 (Diameter of Binary Tree)