题目

给定一个二叉树 root ，返回其最大深度。

二叉树的 最大深度 是指从根节点到最远叶子节点的最长路径上的节点数。

代码

方法一：递归

# 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 0leftdep=self.maxDepth(root.left)rightdep=self.maxDepth(root.right)return max(leftdep,rightdep)+1

方法二：栈迭代

# 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 0stack=[(root,1)]maxdepth=0while stack:node,depth=stack.pop()if node:maxdepth=max(depth,maxdepth)stack.append((node.left,depth+1))stack.append((node.right,depth+1))return maxdepth

方法三：队列迭代

# 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 0queue=deque([root])depth=0while queue:depth+=1# 每进入新的一层depth就加1for _ in range(len(queue)):#将下一层的节点加入队列node=queue.popleft()if node.left:queue.append(node.left)if node.right:queue.append(node.right)return depth