gold-4-2

给定一个有序整数数组，元素各不相同且按升序排列，编写一个算法，创建一棵高度最小的二叉搜索树。

示例:

给定有序数组: [-10,-3,0,5,9],

一个可能的答案是：[0,-3,9,-10,null,5]，它可以表示下面这个高度平衡二叉搜索树：

          0 
         / \ 
 -3 9 
 / / 
 -10 5 

//leetcode submit region begin(Prohibit modification and deletion)
/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public TreeNode sortedArrayToBST(int[] nums) {
        if (nums == null || nums.length == 0) {
            return null;
        }

        return construct(nums, 0, nums.length - 1);
    }

    private TreeNode construct(int[] nums, int from, int to) {
        TreeNode midNode = createMid(nums, from, to);

        if (midNode == null) {
            return midNode;
        }

        int mid = from + (to - from) / 2;

        TreeNode leftN = construct(nums, from, mid - 1);
        TreeNode rightN = construct(nums, mid + 1, to);
        midNode.left = leftN;
        midNode.right = rightN;
        return midNode;
    }



    private TreeNode createMid(int[] nums, int from, int to) {
        if (from > to) {
            return null;
        }

        int mid = from + (to - from) / 2;

        TreeNode newNode = new TreeNode(nums[mid]);

        return newNode;
    }
}
//leetcode submit region end(Prohibit modification and deletion)