function encode(string s)
    string symtab = "abcdefghijklmnopqrstuvwxyz"
    sequence res = {}
    for i=1 to length(s) do
        integer ch = s[i]
        integer k = find(ch,symtab)
        res &= k-1
        for j=k to 2 by -1 do
            symtab[j] = symtab[j-1]
        end for
        symtab[1] = ch
    end for
    return res
end function

function decode(sequence s)
    string symtab = "abcdefghijklmnopqrstuvwxyz"
    string res = ""
    for i=1 to length(s) do
        integer k = s[i]+1
        integer ch = symtab[k]
        res &= ch
        for j=k to 2 by -1 do
            symtab[j] = symtab[j-1]
        end for
        symtab[1] = ch
    end for
    return res
end function

procedure test(string s)
    sequence e = encode(s)
    string d = decode(e)
    ?{s,e,d,{"**ERROR**","ok"}[(s=d)+1]}
end procedure
test("broood")
test("bananaaa")
test("hiphophiphop")