' version 30-03-2017
' compile with: fbc -s console

Data "ABCD", "CABD", "ACDB", "DACB", "BCDA", "ACBD"
Data "ADCB", "CDAB", "DABC", "BCAD", "CADB", "CDBA"
Data "CBAD", "ABDC", "ADBC", "BDCA", "DCBA", "BACD"
Data "BADC", "BDAC", "CBDA", "DBCA", "DCAB"

' ------=< MAIN >=------

Dim As ulong total(3, Asc("A") To Asc("D"))  ' total(0 to 3, 65 to 68)
Dim As ULong i, j, n = 24 \ 4   ' n! \ n
Dim As String tmp

For i = 1 To 23
    Read tmp
    For j = 0 To 3
        total(j, tmp[j]) += 1
    Next
Next

tmp = Space(4)
For i = 0 To 3
    For j = Asc("A") To Asc("D")
        If total(i, j) <> n Then
         tmp[i] = j
        End If
    Next
Next

Print "The missing permutation is : "; tmp

' empty keyboard buffer
While InKey <> "" : Wend
Print : Print "hit any key to end program"
Sleep
End