python3 解法, 执行用时: 532 ms, 内存消耗: 43.7 MB, 提交时间: 2022-11-10 16:57:25

# 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 expandBinaryTree(self, root: Optional[TreeNode]) -> Optional[TreeNode]:
        if root.left: root.left = TreeNode(-1, left=self.expandBinaryTree(root.left))
        if root.right: root.right = TreeNode(-1, right=self.expandBinaryTree(root.right))
        return root

python3 解法, 执行用时: 492 ms, 内存消耗: 43.8 MB, 提交时间: 2022-11-10 16:56:46

# 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 expandBinaryTree(self, root: Optional[TreeNode]) -> Optional[TreeNode]:
        def dfs(father: TreeNode):
            origin_left = father.left
            origin_right = father.right
            if origin_left is not None:
                father.left = TreeNode(val=-1, left=origin_left)
                dfs(origin_left)
            if origin_right is not None:
                father.right = TreeNode(val=-1, right=origin_right)
                dfs(origin_right)

        dfs(root)
        return root