def build(start1, end2, length):
if not length:
return None
root_val = postorder[end2]
root = TreeNode(root_val)
if length == 1:
return root
root_index = inorder.index(root_val)
left_length = root_index - start1
right_length = length - left_length - 1
root.left = build(start1, end2 - right_length - 1, left_length)
root.right = build(start1 + 1 + left_length, end2 - 1,
right_length)
return root
def build(start1, start2, length):
if not length:
return None
root_val = preorder[start1]
root = TreeNode(root_val)
if length == 1:
return root
root_index = inorder.index(root_val)
left_length = root_index - start2
right_length = length - left_length - 1
root.left = build(start1 + 1, start2, left_length)
root.right = build(start1 + 1 + left_length,
start2 + 1 + left_length, right_length)
return root
def sortedListToBST(self, head):
"""
升序链表，转二叉搜索树
:type head: ListNode
:rtype: TreeNode
"""
if not head:
return
if not head.next:
return TreeNode(head.val)
slow, fast = head, head.next.next
while fast and fast.next:
fast = fast.next.next
slow = slow.next
tmp = slow.next
slow.next = None
root = TreeNode(tmp.val)
root.left = self.sortedListToBST(head)
root.right = self.sortedListToBST(tmp.next)
return root