114.二叉树展开为链表.py

# @before-stub-for-debug-begin
from python3problem114 import *
from typing import *
# @before-stub-for-debug-end

#
# @lc app=leetcode.cn id=114 lang=python3
#
# [114] 二叉树展开为链表
#

# @lc code=start
# 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 flatten(self, root: TreeNode) -> None:
        preorderList = list()

        def preorderTraversal(root: TreeNode):
            if root:
                preorderList.append(root)
                preorderTraversal(root.left)
                preorderTraversal(root.right)
        
        preorderTraversal(root)
        size = len(preorderList)
        for i in range(1, size):
            prev, curr = preorderList[i - 1], preorderList[i]
            prev.left = None
            prev.right = curr

# @lc code=end