Convert Sorted List to Binary Search Tree.py

'''
Given a singly linked list where elements are sorted in ascending order, convert it to a height balanced BST.

For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.

Example:

Given the sorted linked list: [-10,-3,0,5,9],

One possible answer is: [0,-3,9,-10,null,5], which represents the following height balanced BST:

      0
     / \
   -3   9
   /   /
 -10  5
'''

# 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
        """
        data = []
        while head:
            data.append(head.val)
            head = head.next
        return self.build(data, 0, len(data) - 1)
    
    def build(self, data, left, right):
        if left > right:
            return None
        mid = (left + right) // 2
        node = TreeNode(data[mid])
        node.left = self.build(data, left, mid - 1)
        node.right = self.build(data, mid + 1, right)
        return node