def build_tree():
val = vals.popleft()
if val != 'null':
node = TreeNode(int(val))
node.left = build_tree()
node.right = build_tree()
return node
else:
return None
def helper(l, r):
nonlocal head # 将head声明为外层变量
if l > r: return None
mid = (l + r) // 2
left = helper(l, mid - 1)
root = TreeNode(head.val)
root.left = left
head = head.next
root.right = helper(mid + 1, r)
return root
def sortedListToBST(self, head):
"""
:type head: ListNode
:rtype: TreeNode
"""
if not head: return None
if not head.next: return TreeNode(head.val)
slow = self.find_mid_node(head)
root = TreeNode(slow.val)
root.left, root.right = self.sortedListToBST(
head), self.sortedListToBST(slow.next)
return root
def helper(n):
if n == 1:
return [TreeNode(0)]
i, res = 1, []
while i < n - 1:
left, right = helper(i), helper(n - 1 - i)
for x in left:
for y in right:
root = TreeNode(0)
root.left = x
root.right = y
res.append(root)
i += 2
return res
def deserialize(self, data):
"""Decodes your encoded data to tree.
:type data: str
:rtype: TreeNode
"""
vals = collections.deque(data.split())
def build_tree():
val = vals.popleft()
if val != 'null':
node = TreeNode(int(val))
node.left = build_tree()
node.right = build_tree()
return node
else:
return None
return build_tree()
# Your Codec object will be instantiated and called as such:
codec = Codec()
t = TreeNode(5)
t.left = TreeNode(2)
t.left.right = TreeNode(4)
t.right = TreeNode(9)
root = codec.deserialize(codec.serialize(t))
Tree().front_recursion(root)
def helper(l, r):
if l > r: return None
mid = (l + r) // 2
root = TreeNode(vals[mid])
root.left, root.right = helper(l, mid - 1), helper(mid + 1, r)
return root
def helper(list):
if not list: return None
mid = len(list) // 2
root = TreeNode(list[mid])
root.left, root.right = helper(list[:mid]), helper(list[mid + 1:])
return root