104.maximum-depth-of-binary-tree.py

#
# @lc app=leetcode id=104 lang=python3
#
# [104] Maximum Depth of Binary Tree
#
# https://leetcode.com/problems/maximum-depth-of-binary-tree/description/
#
# algorithms
# Easy (73.38%)
# Likes:    9509
# Dislikes: 156
# Total Accepted:    2.1M
# Total Submissions: 2.9M
# Testcase Example:  '[3,9,20,null,null,15,7]'
#
# 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, 10^4].
# -100 <= Node.val <= 100
# 
# 
#

# @lc code=start
# 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
        queue = [root]
        depth = 0
        while len(queue) > 0:
            depth += 1
            for _ in range(len(queue)):
                node = queue.pop(0)
                if node.left:
                    queue.append(node.left)
                if node.right:
                    queue.append(node.right)
        return depth
        
# @lc code=end


'''
class Solution:
    def maxDepth(self, root: Optional[TreeNode]) -> int:
        if not root:
            return 0
        return max(self.maxDepth(root.left), self.maxDepth(root.right)) + 1
'''