LeetCode: 104. Maximum Depth of Binary Tree

题目

原题地址：https://leetcode.com/problems/maximum-depth-of-binary-tree/

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:

image

Input: root = [3,9,20,null,null,15,7]
Output: 3

Example 2:

Input: root = [1,null,2]
Output: 2

Example 3:

Input: root = []
Output: 0

Example 4:

Input: root = [0]
Output: 1

Constraints:

  • The number of nodes in the tree is in the range [0, 104].
  • -100 <= Node.val <= 100

解法

求左右子树各自的最大深度，然后进行比较取最大值再加一，即为 root 节点的最大深度。

这个方法的 Python 代码类似下面这样:

# 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):
        if root is None:
            return 0
        return 1 + max(self.maxDepth(root.left), self.maxDepth(root.right))

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