108. Convert Sorted Array to Binary Search Tree

    /*
     * 108. Convert Sorted Array to Binary Search Tree 
     * 2016-5-17 By Mingyang
     */
    public TreeNode sortedArrayToBST(int[] num) {
        if (num.length == 0)
            return null;
        return sortedArrayToBST(num, 0, num.length - 1);
    }
    public TreeNode sortedArrayToBST(int[] num, int start, int end) {
        if (start > end)
            return null;
        int mid = (start + end) / 2;
        TreeNode root = new TreeNode(num[mid]);
        root.left = sortedArrayToBST(num, start, mid - 1);
        root.right = sortedArrayToBST(num, mid + 1, end);
        return root;
    }