104. Maximum Depth of Binary Tree

Given the root of a binary tree, return its maximum depth

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, 10^4].
• -100 <= Node.val <= 100

Approach

Solution

# 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: Optional[TreeNode]) -> int:
        if not root:
            return 0

        return 1 + max(self.maxDepth(root.left), self.maxDepth(root.right))

Explanation