144. Maximum Depth of Binary Tree

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

Output: 3

Explanation: The longest path is 3 -> 20 -> 15 or 3 -> 20 -> 7.

Input: root = [1,null,2]

Output: 2

Explanation: The longest path is 1 -> 2.

Input: root = []

Output: 0

Explanation: An empty tree has a depth of 0.

Time Complexity

N/A

Space Complexity

N/A