easy

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
Explanation: The longest path is 3 -> 20 -> 15 (or 3 -> 20 -> 7), which has 3 nodes.
Example 2
Input: root = [1,null,2]
Output: 2
Explanation: The longest path is 1 -> 2, which has 2 nodes.

Constraints

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