求最大树深（关键词：二叉树/深度/高度/递归/非递归）

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求最大树深

递归算法

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

        # 递归 - 极简 - 开始：
        if root is None:
            return 0
        f = self.maxDepth
        return 1 + max(f(root.left), f(root.right))

1 行：

class Solution:
    def maxDepth(self, root):
        f = self.maxDepth
        return 0 if root is None else 1 + max(f(root.left), f(root.right))

非递归算法

此算法的思路是，层序遍历二叉树，并统计树的层数，即高度。

        if root is None:
            return 0
        
        last_level = [root]
        h = 0
        
        while last_level != []:
            next_level = []
            
            while last_level != []:
                node = last_level.pop()
                
                if node.left is not None:
                    next_level.append(node.left)
                if node.right is not None:
                    next_level.append(node.right)
                
            last_level = next_level
            h += 1
        
        return h

参考文献

1. 这是印象笔记中的笔记，如果是在CSDN手机APP上查看此博客，请在印象笔记手机APP中搜索该参考文献：
   https://app.yinxiang.com/shard/s44/nl/9329661/cf9069c3-cf9d-4f1d-b9d3-8346f19a2ebe；
2. 104. Maximum Depth of Binary Tree - LeetCode；
3. https://leetcode.com/problems/maximum-depth-of-binary-tree/discuss/34198/Python-multiple-solutions-recursion-level-order-using-stack-and-level-order-using-queue；
4. https://leetcode.com/problems/maximum-depth-of-binary-tree/discuss/169751/Python-Recursively-and-Iteratively。