Dim perm_num() As Integer '用來存產生的"排列"組 ex. 當輸入12 perm_num(0)=12 perm_num(0)=21
    Dim perm_count As Integer '
    Sub Main()
        Dim infile As System.IO.StreamReader
        Dim i, tmp As Integer
        Dim arr_len As Integer
        My.Computer.FileSystem.WriteAllText(".\out.txt", "", False) '清空out.txt
        Dim j, k As Integer
        Dim para_str() As String '讀入的參數字串

        '由檔案讀入
        infile = My.Computer.FileSystem.OpenTextFileReader(".\in" & x & ".txt")
            arr_len = infile.ReadLine()
            For y = 0 To arr_len - 1
                para_str = Strings.Split(infile.ReadLine(), " ")
                Dim ar(Len(para_str(0))) As Integer
            j = Integer.Parse(para_str(1))
            k = Integer.Parse(para_str(2))
            For i = 1 To Len(para_str(0))
                ar(i) = Integer.Parse(Mid(para_str(0), i, 1))
            Next

            '輸入數字若為n位數，則有n!種排列
            tmp = 1
            For i = 2 To Len(para_str(0))
                tmp = tmp * i
            Next
            ReDim perm_num(tmp - 1) '重新分配Array大小

            perm_count = 0
            perm(ar, 1, Len(para_str(0))) '產生排列組

            Array.Sort(perm_num) '排序"排列"組(考試不能用內建的函數嗎?)
            My.Computer.FileSystem.WriteAllText(".\out.txt", GCD(perm_num(j - 1), perm_num(k - 1)) & vbCrLf, True)
        Next
            My.Computer.FileSystem.WriteAllText(".\out.txt", vbCrLf, True)

    End Sub

    Function GCD(ByVal x As Integer, ByVal y As Integer) '求最大公因數
        If x Mod y <> 0 Then
            GCD = GCD(y, x Mod y)
        Else
            GCD = y
        End If
    End Function
    Dim tmp_str As String

    'Ref:http://www.blueshop.com.tw/board/FUM20050124191756KKC/BRD20051124010744UJK.html
    Sub perm(ByVal ar() As Integer, ByVal x As Integer, ByVal n As Integer)
        Dim i As Integer
        If x = n + 1 Then
            tmp_str = ""
            For i = 1 To n
                tmp_str = tmp_str & ar(i)
            Next

            perm_num(perm_count) = Integer.Parse(tmp_str) '存到陣列去，用全域變數
            perm_count = perm_count + 1

        End If
        For i = x To n
            swap(ar(x), ar(i))
            perm(ar, x + 1, n)
            swap(ar(x), ar(i))
        Next
    End Sub
    Sub swap(ByRef x As Integer, ByRef y As Integer)
        Dim tmp As Integer
        tmp = x
        x = y
        y = tmp
    End Sub