leetcode_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
给有序数组，创建 平衡二叉搜索树

网友解法：

/** * Definition for a binary tree node. * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */public class Solution {    //  网友方法    public TreeNode sortedArrayToBST(int[] num) {    if (num.length == 0) {        return null;    }    TreeNode head = helper(num, 0, num.length - 1);    return head;}public TreeNode helper(int[] num, int low, int high) {    if (low > high) { // Done        return null;    }    int mid = (low + high) / 2;    TreeNode node = new TreeNode(num[mid]);    node.left = helper(num, low, mid - 1);    node.right = helper(num, mid + 1, high);    return node;}}