小黑开始了拉歌训练，第一次进入部室馆，被通知要去当主持人心里有些紧张的leetcode之旅:337. 打家劫舍 III-编程知识

小黑开始了拉歌训练，第一次进入部室馆，被通知要去当主持人心里有些紧张的leetcode之旅:337. 打家劫舍 III

小黑代码（小黑卡在了bug中，上午一步步探索做出，非常NB!!!）

# 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 rob(self, root: Optional[TreeNode]) -> int:# 递归函数进行动态规划def dfs(node):# 节点为空if not node:return 0, 0, 0# 叶子结点if not (node.left or node.right):return 0, 0, node.val# 动态规划操作first_1, second_1, node1_val = dfs(node.left)first_2, second_2, node2_val = dfs(node.right)third_1 = max(second_1, first_1+node1_val)third_2 = max(second_2, first_2+node2_val)return second_1+second_2, third_1+third_2, node.valfirst_root, second_root, val = dfs(root)return max(second_root, first_root+val)

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动态规划法

# 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 rob(self, root: Optional[TreeNode]) -> int:# 递归函数# 返回[不选择该结点获得收益, 选择该结点获得的收益]def dfs(node):# 结点为空if not node:return [0, 0]# 获得左右结点的数组l = dfs(node.left)r = dfs(node.right)# 不选择该结点not_select = max(l[0], l[1]) + max(r[0], r[1])# 选择该结点select = node.val + l[0] + r[0]return [not_select, select]return max(dfs(root))

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数据库练习

608. 树节点

使用union

# Write your MySQL query statement below
SELECTid, 'Root' AS 'type'
FROMTree
WHEREp_id IS NULLUNIONSELECTid, 'Leaf' AS 'type'
FROMTree
WHEREid NOT IN(SELECTp_idFROMTreeWHEREp_id IS NOT NULL)AND p_id IS NOT NULL
UNIONSELECTid, 'Inner' AS 'type'
FROMTree
WHEREid IN (SELECT DISTINCTp_idFROMTreeWHEREp_id IS NOT NULL)AND p_id IS NOT NULL

Case法（小黑第一次使用，了解了sql中的case的基本用法）

# Write your MySQL query statement below
SELECTid,CASEWHEN tree.p_id IS NULLTHEN 'Root'WHEN tree.id IN (SELECT DISTINCT p_id FROM Tree WHERE p_id IS NOT NULL) AND tree.p_id IS NOT NULLTHEN 'Inner'WHEN tree.id NOT IN (SELECT DISTINCT p_id FROM TREE WHERE p_id IS NOT NULL)THEN 'Leaf'ELSE 'other'END AS Type
FROMTree

IF分支法

# Write your MySQL query statement below
SELECTid,IF(ISNULL(Tree.p_id), 'Root', IF(Tree.id IN (SELECT DISTINCT p_id FROM Tree WHERE p_id IS NOT NULL) AND Tree.p_id IS NOT NULL, 'Inner', 'Leaf')) AS 'type'
FROMTree