sortedArrayToBST.py

#   -*- coding:   utf-8   -*-
'''
Given an array 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 array: [-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
'''
"""
        :type nums: List[int]
        :rtype: TreeNode
        """
# 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 sortedArrayToBST(self, nums):
        if len(nums) == 0:
            return None
        elif len(nums) == 1:
            return TreeNode(nums[0])
        mid = len(nums)//2
        root = TreeNode(nums[mid])
        left = self.sortedArrayToBST(nums[:mid])
        right = self.sortedArrayToBST(nums[mid+1:])
        root.left = left
        root.right = right
        return root

if __name__ == "__main__":
	sol = Solution()
	nums = [0,1,2,3,4,5]
	print(sol.sortedArrayToBST(nums))