538. Convert BST to Greater Tree刷题笔记

问题描述 第一次没做出来，主要问题还是出在递归上
pycharm代码

class Node(object):
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None
# 树生成代码
def generate_tree(vals):
    if len(vals) == 0:
        return None
    que = [] # 定义队列
    fill_left = True # 由于无法通过是否为 None 来判断该节点的左儿子是否可以填充，用一个记号判断是否需要填充左节点
    for val in vals:
        node = Node(val) if val is not None else None # 非空值返回节点类，否则返回 None
        if len(que)==0:
            root = node # 队列为空的话，用 root 记录根结点，用来返回
            que.append(node)
        elif fill_left:
            que[0].left = node
            fill_left = False # 填充过左儿子后，改变记号状态
            if node: # 非 None 值才进入队列
                que.append(node)
        else:
            que[0].right = node
            if node:
                que.append(node)
            que.pop(0) # 填充完右儿子，弹出节点
            fill_left = True #
    return root

root = generate_tree([4,1,6,0,2,5,7,None,None,None,3,None,None,None,8])


# 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 __init__(self):
        self.sum = 0

    def convertBST(self, root):
        if root:
            self.convertBST(root.right)
            self.sum += root.val
            root.val = self.sum
            self.convertBST(root.left)
        return root
print(Solution().convertBST(root))
print("hi")

运行结果：