def sortedListToBST(self, head):
"""
:type head: ListNode
:rtype: TreeNode
"""
if head is None:
return None
elif head.next is None:
return TreeNode(head.val)
total_count = 0
cur_node = head
while cur_node is not None:
cur_node = cur_node.next
total_count += 1
mid_count = int(total_count / 2)
cur_node = head
while mid_count > 1:
cur_node = cur_node.next
mid_count -= 1
root_tree_node = TreeNode(cur_node.next.val)
right_head = cur_node.next.next
cur_node.next = None
root_tree_node.left = self.sortedListToBST(head)
root_tree_node.right = self.sortedListToBST(right_head)
return root_tree_node
def preOrderDes(self, items):
if len(items) == 0:
return None
item = items.pop(0)
if item == "#":
return None
else:
root = TreeNode(int(item))
root.left = self.preOrderDes(items)
root.right = self.preOrderDes(items)
return root
def sortedArrayToBST(self, nums):
"""
:type nums: List[int]
:rtype: TreeNode
"""
if len(nums) == 0:
return None
left = 0
right = len(nums) - 1
mid = left + (right - left) / 2
root_node = TreeNode(nums[mid])
root_node.left = self.sortedArrayToBST(nums[:mid])
root_node.right = self.sortedArrayToBST(nums[mid + 1:])
return root_node
def backTrack(self, start, end):
root_list = []
if start > end:
root_list.append(None)
return root_list
for index in range(start, end + 1):
left_root_list = self.backTrack(start, index - 1)
right_root_list = self.backTrack(index + 1, end)
for left_root in left_root_list:
for right_root in right_root_list:
new_root = TreeNode(index)
new_root.left = left_root
new_root.right = right_root
root_list.append(new_root)
return root_list
def buildTree(self, inorder, postorder):
"""
:type inorder: List[int]
:type postorder: List[int]
:rtype: TreeNode
"""
if len(inorder) == 0:
return None
root_val = postorder[-1]
root_val_index = -1
for index, val in enumerate(inorder):
if val == root_val:
root_val_index = index
break
root_node = TreeNode(root_val)
root_node.left = self.buildTree(inorder[:root_val_index],
postorder[:root_val_index])
root_node.right = self.buildTree(inorder[root_val_index + 1:],
postorder[root_val_index:-1])
return root_node