104.二叉树的最大深度.py

#
# @lc app=leetcode.cn id=104 lang=python
#
# [104] 二叉树的最大深度
#
# https://leetcode-cn.com/problems/maximum-depth-of-binary-tree/description/
#
# algorithms
# Easy (71.12%)
# Likes:    364
# Dislikes: 0
# Total Accepted:    86.1K
# Total Submissions: 121K
# Testcase Example:  '[3,9,20,null,null,15,7]'
#
# 给定一个二叉树，找出其最大深度。
# 
# 二叉树的深度为根节点到最远叶子节点的最长路径上的节点数。
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# 说明: 叶子节点是指没有子节点的节点。
# 
# 示例：
# 给定二叉树 [3,9,20,null,null,15,7]，
# 
# ⁠   3
# ⁠  / \
# ⁠ 9  20
# ⁠   /  \
# ⁠  15   7
# 
# 返回它的最大深度 3 。
# 
#

# @lc code=start
# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
recursive:

class Solution(object):
    def maxDepth(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """

        if not root:return 0
        else:
            return max(self.maxDepth(root.left),self.maxDepth(root.right))+1


iterate:

class Solution(object):
    def maxDepth(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """   
        if not root:return 0
        stack,depth=[(1,root)],1
        while stack:
            cur,node=stack.pop()
            depth=max(depth,cur)
            if node.left:
                stack.append((cur+1,node.left))
            if node.right:
                stack.append((cur+1,node.right))
        return depth
# @lc code=end