Given a singly linked list where elements are sorted in ascending order, convert it to a height balanced BST.
# Definition for singly-linked list.
# class ListNode(object):
# def __init__(self, x):
# self.val = x
# self.next = None
# Definition for a binary tree node.
# class TreeNode(object):
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution(object):
def sortedListToBST(self, head):
"""
:type head: ListNode
:rtype: TreeNode
"""
if head:
pre = None
slow = fast = head
while fast and fast.next:
pre = slow
slow = slow.next
fast = fast.next.next
root = TreeNode(slow.val)
if pre:
pre.next = None
root.left = self.sortedListToBST(head)
root.right = self.sortedListToBST(slow.next)
return root