Method helper

src/com/blankj/easy/_0108/Solution.java:20–27

(int[] nums, int left, int right)

    }

    private TreeNode helper(int[] nums, int left, int right) {
        if (left > right) return null;
        int mid = (left + right) >>> 1;
        TreeNode node = new TreeNode(nums[mid]);
        node.left = helper(nums, left, mid - 1);
        node.right = helper(nums, mid + 1, right);
        return node;
    }

    public static void main(String[] args) {
        Solution solution = new Solution();