【LeetCode】104. Maximum Depth of Binary Tree 解题报告（Python）

原创

负雪明烛 2021-07-14 13:40:03 ©著作权

文章标签 LeetCode 算法 leetcode depth BinaryTree 文章分类 Python 后端开发

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作者：负雪明烛
id： fuxuemingzhu
个人博客： http://fuxuemingzhu.cn/

题目描述

Given a binary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

Note: A leaf is a node with no children.

Example:

Given binary tree [3,9,20,null,null,15,7],

return its depth = 3.

题目大意

求一颗二叉树的高度。

解题方法

方法一：BFS

求树的高度，可以从根节点开始，每次向下走一层，直到所有的节点遍历结束。层数就是高度。

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def maxDepth(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        depth = 0
        que = collections.deque()
        que.append(root)
        while que:
            size = len(que)
            for _ in range(size):
                node = que.popleft()
                if not node:
                    continue
                que.append(node.left)
                que.append(node.right)
            depth += 1
        return depth - 1

方法二：DFS

运用递归，如果该节点是空，那么高度是0。否则树的高度等于 1 +　左子树和右子树高度的最大值。

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def maxDepth(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        if not root:
            return 0
        return 1 + max(self.maxDepth(root.left), self.maxDepth(root.right))