Maximum depth of binary tree

# 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
        q = collections.deque([root])
        res = 0
        while q:
            size = len(q)
            res += 1
            for i in range(size):
                node = q.popleft()
                if node.left:
                    q.append(node.left)
                if node.right:
                    q.append(node.right)

        return res

Maximum Depth of Binary Tree

Difficulty: 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

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