給定一個二叉樹，返回它的 前序 遍歷。

 示例:

輸入: [1,null,2,3]  
   1
    \
     2
    /
   3 

輸出: [1,2,3]

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def preorderTraversal(self, root):
        """
        :type root: TreeNode
        :rtype: List[int]
        """
        def dummy(root,l):
            if not root:
                return 
            result.append(root.val)
            if root.left:
                dummy(root.left,result)
            if root.right:
                dummy(root.right,result)
        result=[]
        dummy(root,result)
        return result
 

執行用時: 44 ms, 在Binary Tree Preorder Traversal的Python3提交中擊敗了98.03% 的使用者

給定一個二叉樹，返回它的 後序 遍歷。

示例:

輸入: [1,null,2,3]  
   1
    \
     2
    /
   3 

輸出: [3,2,1]

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def postorderTraversal(self, root):
        """
        :type root: TreeNode
        :rtype: List[int]
        """
        def dummy(root,l):
            if not root:
                return
            if root.left:
                dummy(root.left,result)
            if root.right:
                dummy(root.right,result)
            result.append(root.val)
        result=[]
        dummy(root,result)
        return result
 

執行用時: 44 ms, 在Binary Tree Postorder Traversal的Python3提交中擊敗了97.88% 的使用者