from typing import List
from lwabish.algorithm.tree import TreeNode, new_tree
tcs = [
(new_tree("3,2,3,null,3,null,1"),),
]
class Solution:
def rob(self, root: TreeNode) -> int:
cache = {}
def cache_or_cal(root: TreeNode):
result = cache.get(root, None)
if result:
return result
else:
result = do_rob(root)
cache[root] = result
return result
def do_rob(root: TreeNode):
if not root:
return 0
sons = cache_or_cal(root.left) + cache_or_cal(root.right)
grand_sons = 0
if root.left:
grand_sons += cache_or_cal(root.left.left) + \
cache_or_cal(root.left.right)
if root.right:
grand_sons += cache_or_cal(root.right.left) + \
cache_or_cal(root.right.right)
from typing import List, NewType
from lwabish.algorithm.tree import TreeNode, new_tree, print_tree
tcs = [
(new_tree("1,3,2,5"), new_tree("2,1,3,null,4,null,7")),
]
class Solution:
def mergeTrees(self, root1: TreeNode, root2: TreeNode) -> TreeNode:
if not root1 and not root2:
return None
if not root1 and root2:
return root2
if not root2 and root1:
return root1
merged = TreeNode(root1.val + root2.val)
merged.left = self.mergeTrees(root1.left, root2.left)
merged.right = self.mergeTrees(root1.right, root2.right)
return merged
if __name__ == '__main__':
solution = Solution()
for tc in tcs:
print_tree(tc[0])
print_tree(tc[1])
print_tree(solution.mergeTrees(*tc))
from typing import List
from lwabish.algorithm.tree import TreeNode, new_tree
tcs = [
(new_tree(','.join(map(lambda x: str(x),
[3, 9, 20, 'null', 'null', 15, 7]))), ),
]
class Solution:
def levelOrder(self, root: TreeNode) -> List[List[int]]:
res = list()
if not root:
return res
def go(root: TreeNode, level):
"""
leve:索引
"""
if len(res) < level + 1:
res.append(list())
res[level].append(root.val)
if root.left:
go(root.left, level + 1)
if root.right:
go(root.right, level + 1)
go(root, 0)
return res
if __name__ == '__main__':
from typing import List
from lwabish.algorithm.tree import TreeNode, new_tree, print_tree
tcs = [
(new_tree("4,2,7,1,3,6,9"), ),
]
class Solution:
def invertTree(self, root: TreeNode) -> TreeNode:
if not root:
return None
root.left, root.right = self.invertTree(root.right), self.invertTree(
root.left)
return root
if __name__ == '__main__':
solution = Solution()
for tc in tcs:
print_tree(solution.invertTree(*tc))
from typing import Deque, List
from collections import deque
from lwabish.algorithm.tree import TreeNode, new_tree
tcs = [
(new_tree(','.join(map(lambda x: str(x),
[3, 9, 20, 'null', 'null', 15, 7]))), ),
(new_tree(','.join(
map(lambda x: str(x), [
1,
2,
'null',
3,
'null',
4,
'null',
5,
]))), )
]
class Solution:
def levelOrder(self, root: TreeNode) -> List[List[int]]:
if not root:
return []
q = deque([root])
level = 0
result = []
while q:
from typing import List
from lwabish.algorithm.tree import TreeNode, new_tree
tcs = [
(new_tree("3, 9, 20, null, null, 15, 7"),),
]
class Solution:
def isSymmetric(self, root: TreeNode) -> bool:
def check(left: TreeNode, right: TreeNode):
if not left and not right:
return True
# 这个if里本有三种情况，但是有一种在上面已经return了
if not left or not right:
return False
return left.val == right.val and check(left.left, right.right) and check(left.right, right.left)
if not root:
return True
return check(root.left, root.right)
if __name__ == '__main__':
solution = Solution()
for tc in tcs:
print(solution.isSymmetric(*tc))
from typing import List
from lwabish.algorithm.tree import TreeNode, new_tree
tcs = [
(new_tree('1,null,2,3'), ),
]
class Solution:
def inorderTraversal(self, root: TreeNode) -> List[int]:
if root is None:
return []
# 从上到下拍扁：左中右
return self.inorderTraversal(
root.left) + [root.val] + self.inorderTraversal(root.right)
if __name__ == '__main__':
solution = Solution()
for tc in tcs:
print(solution.inorderTraversal(*tc))
from typing import List
from lwabish.algorithm.tree import TreeNode, new_tree
tcs = [
(new_tree('3,5,1,6,2,0,8,null,null,7,4'), 5, 1),
]
class Solution:
def lowestCommonAncestor(self, root: 'TreeNode', p: 'TreeNode', q: 'TreeNode') -> 'TreeNode':
# 递归终止
if not root or root.val == p.val or root.val == q.val:
return root
# dfs递归
l = self.lowestCommonAncestor(root.left, p, q)
r = self.lowestCommonAncestor(root.right, q, p)
# 四种情况return不同值
if not l and not r:
return None
if not l:
return r
if not r:
return l
return root
if __name__ == '__main__':
solution = Solution()
for tc in tcs:
print(solution.lowestCommonAncestor(*tc))
from typing import List
from lwabish.algorithm.tree import TreeNode, new_tree, print_tree
tcs = [
(new_tree('1,2,5,3,4,null,6'), ),
(new_tree('1,null,2'), ),
(new_tree('1,null,2,3'), ),
]
class Solution:
def flatten(self, root: TreeNode) -> None:
"""
Do not return anything, modify root in-place instead.
"""
if not root:
return None
def attach_to_leaf(root1, root2):
"""
把root2拼接到root1的尾巴上
"""
if not root1:
return None
if not root1.right:
root1.right = root2
else:
attach_to_leaf(root1.right, root2)
# 对右子树进行深度优先遍历，展平
flattened_right = self.flatten(root.right)
# 对左子树进行深度优先遍历，展平
from typing import List
from lwabish.algorithm.tree import TreeNode, new_tree
from collections import deque
tcs = [(new_tree('3, 9, 20, null, null, 15, 7'), )]
class Solution:
def zigzagLevelOrder(self, root: TreeNode) -> List[List[int]]:
if not root:
return []
q = deque([root])
result = []
# 在普通的层序遍历基础上，增加一个开关表示是否反转即可
reverse = False
while q:
this_level_nodes = []
for i in range(len(q)):
node = q.popleft()
this_level_nodes.append(node.val)
if node.left:
q.append(node.left)
if node.right:
q.append(node.right)
if reverse:
this_level_nodes.reverse()
result.append(this_level_nodes)
reverse = not reverse
return result
from typing import List
from lwabish.algorithm.tree import TreeNode, new_tree, print_tree
tcs = [
(new_tree("1,2,3,4,5"), ),
(new_tree(
"4,-7,-3,null,null,-9,-3,9,-7,-4,null,6,null,-6,-6,null,null,0,6,5,null,9,null,null,-1,-4,null,null,null,-2"
), )
]
class Solution:
"""
官方题解方案
技巧：遍历时更新全局变量
"""
def diameterOfBinaryTree(self, root: TreeNode) -> int:
self.d = 0
def depth(root: TreeNode):
if not root:
return 0
l = depth(root.left)
r = depth(root.right)
# 更新全局最大值
self.d = max(l + r, self.d)
return max(l, r) + 1
depth(root)
import time
from typing import List, NewType
from lwabish.algorithm.tree import TreeNode, new_tree, print_tree
tcs = [(new_tree("-10,9,20,null,null,15,7"), ),
(new_tree("9,6,-3,null,null,-6,2,null,null,2,null,-6,-6,-6"), )]
class Solution:
def maxPathSum(self, root: TreeNode) -> int:
self.max_sum = root.val
# 注意排除负值
def do(root: TreeNode):
if not root:
return 0
# 1. 计算每个节点的贡献值：空节点0，叶节点val，非叶节点val+max(左右)
l = do(root.left)
r = do(root.right)
value = root.val + (max(l, r) if max(l, r) > 0 else 0)
# 2. 用贡献值计算节点的路径和，更新全局变量：val+左贡献+右贡献（仅正贡献）
tmp = root.val + (l if l > 0 else 0) + (r if r > 0 else 0)
print(root.val, l, r, tmp)
if tmp > self.max_sum:
self.max_sum = tmp
return value
do(root)
return self.max_sum
if __name__ == '__main__':