求助， DataGridView中如何动态实现指定的单元格合并？

看看以下的程式码
我的标题是动态的
它能1-3还是1-5 ，还是1氮

问题1
在cellpaint事件是否能用for循环？如何写？

问题2
只需格A1横向合并，其他无需，怎做？

图片结果： http://i105.
程式下载： http://cid-7aa8ce26bddc5545.skydrive.

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Dim dt As New DataTable
        dt.Columns.Add("Car")
        dt.Columns.Add("1")
        dt.Columns.Add("2")
        dt.Columns.Add("3")
        dt.Rows.Add(New Object() {"Toyoda", "A1", "C1", "C1"})
        dt.Rows.Add(New Object() {"Honta", "A1", "A1", "D2"})
        dt.Rows.Add(New Object() {"Falali", "A1", "A1", "A1"})
        dt.Rows.Add(New Object() {"Nisun", "B1", "A1", "A1"})
        DataGridView1.DataSource = dt
    End Sub

    Private Sub DataGridView1_CellPainting(ByVal sender As System.Object, ByVal e As System.Windows.Forms.DataGridViewCellPaintingEventArgs) Handles DataGridView1.CellPainting
        If DataGridView1.Rows.Count > 0 Then

            'If Me.DataGridView1.Columns("1").Index = e.ColumnIndex AndAlso e.RowIndex >= 0 Then
            If e.ColumnIndex = 0 AndAlso e.RowIndex >= 0 Then
                Using gridBrush As Brush = New SolidBrush(Me.DataGridView1.GridColor), backColorBrush As Brush = New SolidBrush(e.CellStyle.BackColor)
                    Using gridLinePen As New Pen(gridBrush)
                        ' 擦除原单元格背景
                        e.Graphics.FillRectangle(backColorBrush, e.CellBounds)

                        If e.Value.ToString() <> Me.DataGridView1.Rows(e.RowIndex).Cells(e.ColumnIndex + 1).Value.ToString() Then

                            '右侧的线
                            e.Graphics.DrawLine(gridLinePen, e.CellBounds.Right - 1, e.CellBounds.Top, e.CellBounds.Right - 1, e.CellBounds.Bottom - 1)
                            '绘制值
                            If e.Value IsNot Nothing Then
                                e.Graphics.DrawString(DirectCast(e.Value, [String]), e.CellStyle.Font, Brushes.Crimson, e.CellBounds.X + 2, e.CellBounds.Y + 2, StringFormat.GenericDefault)
                            End If
                        End If

                        '下边缘的线
                        e.Graphics.DrawLine(gridLinePen, e.CellBounds.Left, e.CellBounds.Bottom - 1, e.CellBounds.Right - 1, e.CellBounds.Bottom - 1)
                        e.Handled = True
                    End Using

                End Using

            End If

        End If
    End Sub