【LeetCode】二叉树的递归遍历

题目

1. 给你二叉树的根节点 root ，返回它节点值的 前序 遍历。

算法与思路

Preorder traversal order:

1. Visit the current node.
2. Traverse the left subtree.
3. Traverse the right subtree.
   
   

Returns:
list: A list of integers representing the preorder traversal.

代码

1. 前序

   # 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 preorderTraversal(self, root: Optional[TreeNode]) -> List[int]:
           if not root:
               return []
           return [root.val] + self.preorderTraversal(root.left) + self.preorderTraversal(root.right)
           
   

2. 中序（同理）

   # 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 inorderTraversal(self, root: Optional[TreeNode]) -> List[int]:
           if not root:
               return []
           return self.inorderTraversal(root.left) + [root.val] + self.inorderTraversal(root.right)
       
   

3. 后序（同理）

   class Solution:
   def postorderTraversal(self, root: Optional[TreeNode]) -> List[int]:
       if not root:
           return []
       return self.postorderTraversal(root.left) + self.postorderTraversal(root.right) + [root.val]
   

总结