def deserialize_tree(s):
if not s:
return
val = s.pop(0)
root = None
if val != 'null':
root = TreeNode(val)
root.left = deserialize_tree(s)
root.right = deserialize_tree(s)
return root
def build1(inorder, postorder):
if not inorder:
return None
elif len(inorder) == 1:
return TreeNode(inorder[0])
else:
postorder_root_val = postorder[-1]
root = TreeNode(postorder_root_val)
for i in range(len(inorder)):
if postorder_root_val == inorder[i]:
inorder_root_index = i
break
if inorder_root_index == 0:
root.left = None
root.right = build1(inorder[1:], postorder[:-1])
elif inorder_root_index == len(inorder) - 1:
root.left = build1(inorder[:-1], postorder[:-1])
root.right = None
else:
root.left = build1(inorder[:inorder_root_index],
postorder[:inorder_root_index])
root.right = build1(inorder[inorder_root_index + 1:],
postorder[inorder_root_index:-1])
return root
def build1(preorder, inorder):
if not preorder:
return None
if len(preorder) <= 1:
return TreeNode(preorder[0])
root_node = preorder[0]
root = TreeNode(root_node)
for i in range(len(inorder)):
if root_node == inorder[i]:
inorder_root_node_index = i
break
root.left = build1(preorder[1:inorder_root_node_index + 1],
inorder[:inorder_root_node_index])
root.right = build1(preorder[inorder_root_node_index + 1:],
inorder[inorder_root_node_index + 1:])
return root
def before_middle_construct_tree(before_seq, middle_seq):
"""
根据二叉树的前序遍历和中序遍历重建二叉树
:param before_seq: List[int]
:param middle_seq: List[int]
:return: TreeNode
"""
if len(before_seq) == 0 or len(middle_seq) == 0:
return
root_node = TreeNode(before_seq[0])
root_index = middle_seq.index(root_node.val)
left_node = before_middle_construct_tree(before_seq[1:root_index + 1],
middle_seq[:root_index])
right_node = before_middle_construct_tree(before_seq[root_index + 1:],
middle_seq[root_index + 1:])
root_node.left = left_node
root_node.right = right_node
return root_node
# 非递归方式解法，父亲节点的元组中第一个元素为0，孩子节点的元组中第一个元素为1
res = []
s = [(1, root)] # 0表示不可以往下遍历，1表示可以往下继续遍历
while s:
p = s.pop()
if not p[1]: # 判断某个节点为空
continue
if p[0]: # 判断为子节点的话，就继续往栈里面放数据
s.extend([(1, p[1].right), (0, p[1]), (1, p[1].left)])
else: # 判断为主节点的话，就说明其左节点已经为空了，那么该父节点可以输出到数组中了
res.append(p[1].val)
return res
if __name__ == "__main__":
"""
1
4 2
3 6
"""
root = TreeNode(1)
root.left = layer2_left = TreeNode(4)
root.right = layer2_right = TreeNode(2)
layer2_left.left = TreeNode(3)
layer2_left.right = TreeNode(6)
# print(tree_in_order_traversal(root))
# res = []
# tree_in_order_traversal1(root, res)
# print(res)
print(tree_in_order_traversal2(root))
elif nums[low] + nums[high] < k:
low += 1
else:
return True
return False
if __name__ == "__main__":
"""
5
/ \
3 6
/ \ \
2 4 7
Target = 9
"""
root = TreeNode(5)
root.left = layer2_left = TreeNode(3)
root.right = layer2_right = TreeNode(6)
layer2_left.left = TreeNode(2)
layer2_left.right = TreeNode(4)
layer2_right.right = TreeNode(7)
target = 9
print(two_sum_iv_input_bst(root, k=target))
# root = root.left
# return res
# return pre_traverse(root)
# Solution3
def is_symmetrical(root1, root2):
if not root1 and not root2:
return True
if not root1 or not root2:
return False
if root1.val != root2.val:
return False
return is_symmetrical(root1.left, root2.right) and is_symmetrical(
root1.right, root2.left)
if not root:
return True
return is_symmetrical(root.left, root.right)
if __name__ == "__main__":
root = TreeNode(1)
root.left = layer2_left = TreeNode(4)
root.right = layer2_right = TreeNode(4)
layer2_left.right = layer3_left_left = TreeNode(6)
layer2_left.left = layer3_left_right = TreeNode(3)
layer2_right.right = layer3_right_left = TreeNode(3)
layer2_right.left = layer3_right_right = TreeNode(6)
print(symmetrical_tree(root))
return 0
left = max(helper(node.left), 0) # 如果有加和为负值的左路径，就直接省略了
right = max(helper(node.right), 0) # 如果有加和为负值的右路径，就直接省略了
self.res = max(self.res, left + right + node.val)
return max(left, right) + node.val
helper(root)
return self.res
if __name__ == "__main__":
"""
-10
20 9
15 7
上面的和最大路径就是 15-20-7，最大和为42
"""
root = TreeNode(-10)
root.left = layer2_left = TreeNode(20)
root.right = layer2_right = TreeNode(9)
layer2_left.left = layer3_left1 = TreeNode(15)
layer2_left.right = layer3_right1 = TreeNode(7)
layer2_right.left = None
layer2_right.right = None
layer3_left1.left = None
layer3_left1.right = None
layer3_right1.left = None
layer3_right1.right = None
solu = Solution()
print(solu.binary_tree_maximum_path_sum(root))
def layerTraverse(root):
node_a = []
if root:
node_a.append(root)
while node_a:
root = node_a.pop(0)
print(root.val)
if root.left:
node_a.append(root.left)
if root.right:
node_a.append(root.right)
if __name__ == "__main__":
root = TreeNode(1)
root.left = layer2_left = TreeNode(2)
root.right = layer2_right = TreeNode(3)
layer2_left.left = layer31_left = TreeNode(4)
layer2_left.right = layer31_right = TreeNode(5)
layer2_right.left = layer32_left = TreeNode(6)
layer2_right.right = layer32_right = TreeNode(7)
layerTraverse(root)
invertTree(root)
print('\n')
layerTraverse(root)
:return: List[int]
"""
def find_(root, target, path, cur_sum, res):
cur_sum += root.val
path.append(root.val)
is_leaf = not root.left and not root.right
if cur_sum == target and is_leaf:
res.append(path + [])
if root.left:
find_(root.left, target, path, cur_sum, res)
if root.right:
find_(root.right, target, path, cur_sum, res)
path.pop() # 跳出本次递归之前需要复原path
cur_sum -= root.val # 跳出本次递归之前需要复原cur_sum
if not root:
return
res = []
find_(root, target, [], 0, res)
return res
if __name__ == "__main__":
root = TreeNode(10)
root.left = layer2_left = TreeNode(5)
root.right = layer2_right = TreeNode(12)
layer2_left.left = TreeNode(4)
layer2_left.right = TreeNode(7)
print(find_path(root, 22))