leetcode-104 - Maximum Depth of Binary Tree

動機

複習dfs

Problem

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:

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

Sol

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