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:

1 2	Input: root = [3,9,20,null,null,15,7] Output: 3

Example 2:

1 2	Input: root = [1,null,2] Output: 2

Example 3:

1 2	Input: root = [] Output: 0

Example 4:

1 2	Input: root = [0] Output: 1

Tree中找最大深度，遞迴尋訪左右子樹，看哪個較深

T: O(n), S: O(1)
# Definition for a binary tree node.
# class TreeNode:
#     def init(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def maxDepth(self, root: TreeNode) -> int:
        if root == None:
            return 0
        return 1 + max(self.maxDepth(root.left), self.maxDepth(root.right))

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