leetcode 109. Convert Sorted List to Binary Search Tree

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题目链接：leetcode

思路：
把链表转成数组，再用递归生成树。

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# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def get_midnode(self,arr):
        if not arr:return None
        mid = len(arr)//2
        node = TreeNode(arr[mid])
        node.left = self.get_midnode(arr[:mid])
        node.right = self.get_midnode(arr[mid+1:])
        return node
    def sortedListToBST(self, head):
        """
        :type head: ListNode
        :rtype: TreeNode
        """
        node,arr=head, []
        while node:
            arr.append(node.val)
            node = node.next
        return self.get_midnode(arr)