1. (2021·浙江模拟) 在图像编码的算法中，需要将一个给定的方形矩阵进行Z字形扫描(Zigzag Scan)，以获得更好的压缩比。给定一个n×n的矩阵，Z字形扫描的过程如下图所示：

经过扫描后得到的数据结果为：

57	45	0	23	0	0	0	0
0	0	0	0	0	0	0	0
0	-30	1	0	0	0	0	0
-16	0	0	0	0	0	0	0
0	0	0	0	0	0	0	0
0	0	0	0	0	0	0	0
0	0	0	0	0	0	0	0
0	0	0	0	0	0	0	0

“57,45,0,0,0,0,23,0,-30,-16,0,0,1,0,0,0,0,…,0,0”，数据元素个数为64个。进一步经过压缩后，最终得到行程编码：“57, 1, 45, 1, 0, 4, 23, 1, 0, 1,-30, 1,-16, 1, 0, 2, 1, 1, 0, 51”,数据元素个数为20个。

1. （1） 行程编码压缩最坏情况下，数据压缩后数据元素的数量将是原来的倍。
3. （2） 根据上述扫描算法，其 VB 代码实现如下，请在划线处填入合适的代码。

   Dim a(0 To 1000) As Integer     '存储原矩阵数据，按行优先存储

   Dim b(0 To 1000) As Integer     '存储Z形扫描后数据

   Dim c(0 To 1000) As Integer     '存储行程编码压缩后数据

   Dim n As Integer

   ‘矩阵导入代码略，以行优先存储在a数组中，如例子中数据存储顺序为“57,45,0,23,0,0…”

   Private Sub Command2_Click()

       Dim choice As Integer     ' 1：向右移动 ；2：向右上移动；3向下移动 4向左下移动

       Dim row As Integer, col As Integer, i As Integer, j As Integer

       Dim pre As Integer, count As Integer

       choice = 1: row = 0: col = 0: i = 0

       Do While (row <> n - 1 Or col <> n - 1)

           b(i) = a(row * n + col):i = i + 1     

           If choice = 1 Then

               

               If row = 0 Then choice = 4 Else choice = 2

           ElseIf choice = 2 Then

               row = row - 1: col = col + 1

               If  Then

                   choice = 1

               ElseIf col = n - 1 Then

                   choice = 3

               End If

           ElseIf choice = 3 Then

               row = row + 1

               If col = 0 Then choice = 2 Else choice = 4

               ElseIf choice = 4 Then

                   row = row + 1: col = col - 1

               If row = n - 1 Then

                   choice = 1

               ElseIf col = 0 Then

                   choice = 3

               End If

           End If

       Loop

       b(i) = a(n * n - 1):j = 0: pre = b(0): count = 0

       For i = 0 To n * n - 1                 '输出Z形序列，并进行行程压缩

           If pre = b(i) Then

               count = count + 1

           Else

               c(j) = pre: c(j + 1) = count

               

               pre = b(i):j = j + 2

           End If

       Next i

       c(j) = pre: c(j + 1) = count

       Text1.Text = ""

       For i = 0 To j + 1

           Text1.Text = Text1.Text + Str(c(i)) + ","

       Next i

   End Sub