JZTXT

day13 代码随想录算法训练营 递归遍历

发布时间 2024-01-10 13:51:57作者: o蹲蹲o

题目：

我的感悟：

  • 用helper内部函数写更好

理解难点：

 

代码难点：

代码示例：

  • 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]:
        res = []
        def helper(root):
            if not root:return 
            res.append(root.val)
            helper(root.left)
            helper(root.right)
        helper(root)
        return res
  • 中序
  • # 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]:
        res = []
        def helper(root):
            if not root:return             
            helper(root.left)
            res.append(root.val)    # 结果放在这里,中序
            helper(root.right)
        helper(root)
        return res
  • 后序
  • # 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]:
        res = []
        def helper(root):
            if not root:return             
            helper(root.left)             
            helper(root.right)
            res.append(root.val)  # 结果放在后面,后序 
        helper(root)
        return res

通过截图：

扩展写法：

资料：

https://programmercarl.com/%E4%BA%8C%E5%8F%89%E6%A0%91%E7%9A%84%E9%80%92%E5%BD%92%E9%81%8D%E5%8E%86.html#%E6%80%9D%E8%B7%AF