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.

递归

/**
 * 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) {
        return sortedArrayToBST(nums, 0, nums.length - 1);
    }

    public TreeNode sortedArrayToBST(int[] nums, int start, int end) {
        if(start > end)
            return null;

        if(start == end)
            return new TreeNode(nums[start]);

        int mid = start + (end - start) / 2;
        TreeNode root = new TreeNode(nums[mid]);
        TreeNode left = sortedArrayToBST(nums, start, mid - 1);
        TreeNode right = sortedArrayToBST(nums, mid + 1, end);
        root.left = left;
        root.right = right;
        return root;
    }
}