def insert(self, v: int) -> int:
n = len(self.memo)
p_node = self.memo[(n - 1) // 2]
if n % 2 == 1: # adds left child
p_node.left = TreeNode(v)
self.memo.append(p_node.left)
else: # adds right child
p_node.right = TreeNode(v)
self.memo.append(p_node.right)
return p_node.val
def invert_tree(self, root: TreeNode) -> TreeNode:
'''
翻转二叉树
Args:
root: 根节点
Returns:
TreeNode
'''
if root == None:
return None
left = self.invert_tree(root.left)
right = self.invert_tree(root.right)
root.left = right
root.right = left
return root
def deserialize(self, data: str) -> TreeNode:
if not data or data == '[]': return None
data = data[1:-1].split(',')
root = TreeNode(int(data[0]))
idx, queue = 0, [root]
while queue:
cur = queue.pop(0)
if idx * 2 + 1 < len(data) and data[idx * 2 + 1] != 'null':
cur.left = TreeNode(int(data[idx * 2 + 1]))
queue.append(cur.left)
if idx * 2 + 2 < len(data) and data[idx * 2 + 2] != 'null':
cur.right = TreeNode(int(data[idx * 2 + 2]))
queue.append(cur.right)
idx += 1
return root
def flatten_for_list(self, root: TreeNode, current_node) -> TreeNode:
'''
循环递归树
Args:
root: 根节点
current_node: 当前节点
Returns:
root
'''
if not root:
return current_node
current_node = self.flatten_for_list(root.right, current_node)
current_node = self.flatten_for_list(root.left, current_node)
root.left = None
root.right = current_node
return root
def merge_trees(t1: TreeNode, t2: TreeNode) -> TreeNode:
'''
合并两棵二叉树
Args:
t1: 二叉树t1
t2: 二叉树t2
Returns:
合并后的二叉树
'''
if t1 == None:
return t2
if t2 == None:
return t1
t1.val += t2.val
t1.left = merge_trees(t1.left, t2.left)
t1.right = merge_trees(t1.right, t2.right)
return t1
def insert(tree: TreeNode, data):
if tree is None:
return TreeNode(data)
p = tree
if data > p.val:
if p.right is None:
p.right = TreeNode(data)
return tree
else:
return BinarySearchTree.insert(p.right, data)
else: # data <= p.val
if p.left is None:
p.left = TreeNode(data)
return tree
else:
return BinarySearchTree.insert(p.left, data)
def insert_iterative(tree: TreeNode, data):
if tree is None:
return TreeNode(data)
p = tree
while p is not None:
if data > p.val:
if p.right is None:
p.right = TreeNode(data)
return tree
else:
p = p.right
else: # data <= p.val
if p.left is None:
p.left = TreeNode(data)
return tree
else:
p = p.left
def convert_bst(self, root: TreeNode) -> TreeNode:
'''
二分查找树
Args:
root: 根节点
Returns:
节点的值
'''
global total_sum
if not root:
self.convert_bst(root.right)
total_sum += root.val
root.val = total_sum
self.convert_bst(root.left)
return root
def max_depth(root: TreeNode):
if not root: return 0
q = [root]
step = 1
all_step = []
while q:
n = len(q)
for _ in range(n):
node = q.pop(0)
if not node:
continue
if not node.left and not node.right:
all_step.append(step)
q.append(node.left)
q.append(node.right)
step += 1
return max(all_step)
t = TreeNode(3)
t.left = TreeNode(9)
t.right = TreeNode(20)
t.right.left = TreeNode(15)
t.right.right = TreeNode(7)
print(min_depth(t))
print(max_depth(t))
root: 根节点
'''
if root.left:
self.helper(result, root.left)
if root.right:
self.helper(result, root.right)
result.append(root.val)
def post_order_traversal(self, root: TreeNode) -> List[int]:
'''
后序遍历
Args:
res: 链表
root: 根节点
'''
result = []
if not root:
return result
self.helper(result, root)
return result
if __name__ == '__main__':
arr = [1, 2, 3, 4, 5]
tree_node = TreeNode()
tree = tree_node.create_binary_tree_array(arr)
solution = Solution()
result = solution.post_order_traversal(tree)
print(result)
assert result[len(result) - 1] == 1
Returns:
布尔值
'''
queue = []
queue.append(root)
queue.append(root)
while queue:
r1 = queue.pop()
r2 = queue.pop()
if not r1 and not r2:
continue
if not r1 or not r2:
return False
if r1.val != r2.val:
return False
queue.append(r1.left)
queue.append(r2.right)
queue.append(r1.right)
queue.append(r2.left)
return True
if __name__ == '__main__':
arr1 = [1, 2, 2]
tree_node = TreeNode()
root = tree_node.create_binary_tree_array(arr1)
solution = Solution()
result = solution.is_symmetric2(root)
print(result)
assert result == True
def build(self, array, p, q):
nodes = {}
for v in array:
if v != None:
nodes[v] = TreeNode(v)
return nodes, nodes[p], nodes[q]
Google: 90% of our engineers use the software you wrote (Homebrew), but you can’t invert a binary tree on a whiteboard so f*** off.
"""
from tree.tree_node import TreeNode
def invert_binary_tree(root: TreeNode):
if not root:
return None
stack = [root] # stack存放还没有做对换的节点
while stack:
node = stack.pop()
if not node:
continue
node.left, node.right = node.right, node.left
stack.append(node.left)
stack.append(node.right)
return root
t = TreeNode(4)
t.left = TreeNode(2)
t.left.left = TreeNode(1)
t.left.right = TreeNode(3)
t.right = TreeNode(7)
t.right.left = TreeNode(6)
t.right.right = TreeNode(9)
print(invert_binary_tree(t))
'''
if t1 == None:
return t2
if t2 == None:
return t1
stack = []
stack.append((t1, t2))
while stack:
t = stack.pop()
if t[0] == None or t[1] == None:
continue
t[0].val += t[1].val
if t[0].left == None:
t[0].left = t[1].left
else:
stack.append((t[0].left, t[1].left))
if t[0].right == None:
t[0].right = t[1].right
else:
stack.append((t[0].right, t[1].right))
return t1
if __name__ == '__main__':
tree_node = TreeNode()
t1 = tree_node.create_binary_tree_array([1, 2, 3], 0)
t2 = tree_node.create_binary_tree_array([1, 2, 3], 0)
t = merge_trees2(t1, t2)
t_arr = per_order_traversal(t)
print(t_arr)
root: 节点root
p: 节点p
q: 节点q
Returns:
最小公共祖先
'''
if not root:
return root
if not p or not q:
return root
left = lowest_common_ancestor(root.left, p, q)
right = lowest_common_ancestor(root.right, p, q)
if not left and not right:
return None
if left and right:
return root
if not left:
return right
else:
return left
if __name__ == '__main__':
nums = [3, 5, 1, 6, 2, 0, 8, None, None, 7, 4]
tree_node = TreeNode()
p = TreeNode(5)
q = TreeNode(1)
root = tree_node.create_binary_tree_array(nums)
result = lowest_common_ancestor(root, p, q)
print(result)
@staticmethod
def height(root: TreeNode):
if root is None:
return 0
else:
# compute the height of each subtree
l_height = BinaryTreeTraversal.height(root.left)
r_height = BinaryTreeTraversal.height(root.right)
# return the larger one
return max(l_height, r_height) + 1
if __name__ == '__main__':
# construct a binary tree
d = TreeNode('d')
e = TreeNode('e')
f = TreeNode('f')
g = TreeNode('g')
b = TreeNode('b', d, e)
c = TreeNode('c', f, g)
a = TreeNode('a', b, c)
# traverse the binary via different approaches
print('pre-order:', end='\t\t')
BinaryTreeTraversal.pre_order(a)
print('\nin-order:', end='\t\t')
BinaryTreeTraversal.in_order(a)
self.in_order(root.left)
if self.pre and self.pre.val > root.val:
if not self.first: self.first = self.pre
self.second = root
self.pre = root
self.in_order(root.right)
def recover_tree(self, root: TreeNode):
self.in_order(root)
self.first.val, self.second.val = self.second.val, self.first.val
r = TreeNode(3)
r.left = TreeNode(1)
r.right = TreeNode(4)
r.right.left = TreeNode(2)
recover = RecoverTree()
recover.recover_tree(r)
def invert_tree2(self, root: TreeNode) -> TreeNode:
'''
翻转二叉树
Args:
root: 根节点
Returns:
TreeNode
'''
if root == None:
return None
node_list = []
node_list.append(root)
while len(node_list) > 0:
cur = node_list.pop()
if cur.left:
node_list.append(cur.left)
if cur.right:
node_list.append(cur.right)
temp = cur.right
cur.right = cur.left
cur.left = temp
return root
if __name__ == '__main__':
arr = [4, 2, 7, 1, 3, 6, 9]
root = TreeNode.create_binary_tree_array(arr)
solution = Solution()
result = solution.invert_tree(root)
assert 4 == result.val
elif p.right is not None:
child = p.right
if pp is None:
tree = child
elif pp.left == p:
pp.left = child
else:
pp.right = child
return tree
if __name__ == '__main__':
# construct a binary tree
m_19 = TreeNode(19)
n_27 = TreeNode(27)
o_55 = TreeNode(55)
h_15 = TreeNode(15)
i_17 = TreeNode(17)
j_25 = TreeNode(25, m_19, n_27)
k_51 = TreeNode(51, right=o_55)
l_66 = TreeNode(66)
d_13 = TreeNode(13, right=h_15)
e_18 = TreeNode(18, i_17, j_25)
f_34 = TreeNode(34)
g_58 = TreeNode(58, k_51, l_66)
b_16 = TreeNode(16, d_13, e_18)
def is_valid_BST_2(self, root: TreeNode) -> bool:
'''
中序遍历二叉树判断是不是BST树
Args:
root: 根节点
Returns:
布尔值
'''
pre = -sys.maxsize
stack = []
while not root or len(stack) < 1:
while not root.left:
stack.append(root.left)
root = root.left
# 栈退出一个元素
root = stack.pop()
if root.val <= pre:
return False
pre = root.val
root = root.right
return True
if __name__ == '__main__':
nums = [2, 1, 3]
tree = TreeNode()
root = tree.create_binary_tree_array(nums)
solution = Solution()
result = solution.is_valid_BST(root)
assert result == True