leetcode之Convert Sorted List to Binary Search Tree

这道题的思路借鉴了将esorted array转换的思路。讲linked list转换为array。再来做。代码如下：

# 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
        """
        listofall = []
        while head:
            listofall.append(head.val)
            head = head.next
        def sortedArrayToBST(nums):
            length = len(nums)
            if length == 0:
                return None
            if length == 1:
                return TreeNode(nums[0])
            if length == 2:
                root = TreeNode(nums[0])
                root.right = TreeNode(nums[1])
            if length == 3:
                root = TreeNode(nums[1])
                root.left = TreeNode(nums[0])
                root.right = TreeNode(nums[2])
                return root
            root = TreeNode(nums[length / 2])
            root.left = sortedArrayToBST(nums[:length / 2])
            root.right = sortedArrayToBST(nums[length / 2 + 1:])
            return root
        return sortedArrayToBST(listofall)