[Solved] 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.

Question

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

Python 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
mx = 0
def find_max(root,level):
    global mx
    if root==None:return
    mx = max(mx,level)
    find_max(root.left,level+1)
    find_max(root.right,level+1)


class Solution:
    def maxDepth(self, root: TreeNode) -> int:
        global mx
        mx = 0
        find_max(root,1)
        return mx