LeetCode OJ 108. Convert Sorted Array to Binary Search Tree

Given an array where elements are sorted in ascending order, convert it to a height balanced BST.

把一个有序的数组转换为一颗平衡二叉搜索树。每次找到中间节点作为根节点，根节点左边部分转换为左子树，右边部分转换为右子树。代码如下：

 /**
  * Definition for a binary tree node.
  * public class TreeNode {
  *     int val;
  *     TreeNode left;
  *     TreeNode right;
  *     TreeNode(int x) { val = x; }
  * }
  */
 public class Solution {
     public TreeNode sortedArrayToBST(int[] nums) {
         if(nums.length == 0) return null;
         return changeToBST(nums, 0, nums.length-1);
     }

     public TreeNode changeToBST(int[] nums, int left, int right){
         int mid = (right - left)/2 + left;
         TreeNode root = new TreeNode(nums[mid]);
         if(left==mid) root.left = null;
         else root.left = changeToBST(nums, left, mid-1);
         if(right==mid) root.right = null;
         else root.right = changeToBST(nums, mid+1, right);
         return root;
     }
 }