题目：
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
思路：
首先找到数组中间位置的结点，并以此创建一个新的跟结点。向两边递归。注意当开始和结束位置一样时返回null。
代码：
public TreeNode sortedArrayToBST(int[] nums) {
if(nums == null || nums.length == 0)
return null;
return findNode(nums, 0, nums.length);
}
private TreeNode findNode(int[] nums, int begin, int end){
if(begin == end)
return null;
int n = (end + begin)/2;
TreeNode root = new TreeNode(nums[n]);
root.left = findNode(nums, begin, n);
root.right = findNode(nums, n+1, end);
return root;
}
