leetcode-94 - Binary Tree Inorder Traversal

動機

中序的英文是inorder，一開始寫以為是前序

Problem

Given the root of a binary tree, return the inorder traversal of its nodes' values.

Example 1:

Input: root = [1,null,2,3]Output: [1,3,2]

Example 2:

Input: root = []Output: []

Example 3:

Input: root = [1]Output: [1]

Example 4:

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

Example 5:

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

Constraints:

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

Sol

class Solution:
    def inorderTraversal(self, root: TreeNode) -> List[int]:
        ret = []
        def dfs(r):
            if r:
                dfs(r.left)
                ret.append(r.val)
                dfs(r.right)
        dfs(root)
        return ret