IJKLMNOPQRSTUVWXYZ”,转换成5行的“N”字形排列如图所示：

小张根据排列规律设计了“N”字形排列显示的VB程序，功能如下:在文本框Text1中输入原字符串，在文本框Text2中输入“N”字形的行数row(row大于等于3).单击“转换”按钮Command1后，将字符串沿“N”字形排列显示在列表框List1中。程序运行如图所示。

Dim a(1 To 15) As Integer

Private Sub Form_Load()

  Dim i As Integer, t As Integer

  Dim s1 As String, s2 As String

  Randomize

  s1 = ""

  For i = 1 To 15

    a(i) =  ①    

    s1 = s1 + Str(a(i))

  Next i

  Text1.Text = s1

End Sub

Private Sub Com1_Click()

  s2 = ""

  For i = 1 To 15

    s2 =  ②    

  Next i

  Text2.Text = s2

End Sub

def bin(n):

    if n==0:

        return

    else:

        bin(n//2)

    print(n%2,end='')

bin(13)