As
GotToBTru says, the process for mapping your input string to your output string is not clear. See
How do I post a question effectively?. Can you wrap your input and output strings in
<code> tags and describe in English or pseudocode the steps to go from
abcd| a a7- to
[a] [a7] [a], or however that is supposed to be?
#11929 First ask yourself `How would I do this without a computer?' Then have the computer do it the same way.