Rot 13 Minimal Version Java

Question

I tried to implement Rot13 and to make it as minimal as possible, this are my results so far:

    if ( (c >= 'A') && (c <= 'Z') ) 
        c=((c-'A'+13)%26)+'A';

    if ( (c >= 'a') && (c <= 'z') )
        c=((c-'a'+13)%26)+'a';

    return c;

I showed this to my Prof and he said it would be possible in two lines. I don't know how i could shrink this code further and not generating wrong output.

Thanks for your help

EDIT: if nothing changed (outer range ascii) it should only return c. Maybe the solution is the second answer + return line c in case nothing returned.

Answer 1

Slightly more correct than Sibbo's answer. This returns c as is if it falls in neither range. and in 1 line.

return ((c >= 'A') && (c <= 'Z')) ? ((c-'A'+13)%26)+'A'
                                 :((c >= 'a') && (c <= 'z') ? ((c-'a'+13)%26)+'a'
                                                                  : c);

Answer 2

You don't need to update c; just return:

if ((c >= 'A') && (c <= 'Z')) {
    return ((c - 'A' + 13) % 26) + 'A';
}

if ((c >= 'a') && (c <= 'z')) {
    return ((c - 'a' + 13) % 26) + 'a';
}

I also made the code more readable.

This could easily be made into two lines:

if ((c >= 'A') && (c <= 'Z')) return ((c - 'A' + 13) % 26) + 'A';
if ((c >= 'a') && (c <= 'z')) return ((c - 'a' + 13) % 26) + 'a';

Or one:

if ((c >= 'A') && (c <= 'Z')) return ((c - 'A' + 13) % 26) + 'A'; if ((c >= 'a') && (c <= 'z')) return ((c - 'a' + 13) % 26) + 'a';

But of course, that is much less readable, and not a good idea.

Answer 3

One line:

return (c < 'a') ? ((c - 'A' + 13) % 26) + 'A' : ((c - 'a' + 13) % 26) + 'a';

This simply makes use of the fact that lower case letters come after upper case letters in ASCII and UTF-8. Of course, it doesn't verify the input in any way.

Answer 4

There is a little trick using the ASCII table. Upper and lower case chars only differ one bit. So you could handle them at once. Take a look at this:

A = 0100 0001     M = 0100 1101
a = 0110 0001     m = 0110 1101

So, I think this should work:

if (Character.isLetter(c))
   return (char) ((((c & 0b01011111) - 'A' + 13) % 26 + 'A') | (c & 0b00100000));
return c;

Explanation:

1. c & 0b01011111 turns the char into an uppercase.
2. - 'A' + 13 converts to an 0-based int and applies the offset.
3. % 26 + 'A' Take the modulo and make it back a char.
4. (c & 0b00100000) takes the bit that indicates wether the char was lower case or not.
5. | Add that bit back to the result to make it lowercase if it was.

You could use the conditional operator here to make it a one-liner:

return Character.isLetter(c) ? (char) ((((c & 0b01011111) - 'A' + 13) % 26 + 'A') | (c & 0b00100000)) : c;

After replacing the binary and char literals by decimal int literals, you get:

return Character.isLetter(c) ? (char) ((((c & 95) - 52) % 26 + 65) | (c & 32)) : c;

Eliminating spaces and some extra brackets gives: (65 chars)

return Character.isLetter(c)?(char)((((c&95)-52)%26+65)|c&32):c;

Which is a win, IMHO, if it comes to code golfing. This is of course not readable.

---

Demo: Yep, confirmed. It works: http://ideone.com/l6xYy6

Excerpt from the output:

= -> =
> -> >
? -> ?
@ -> @
A -> N
B -> O
C -> P
D -> Q

And a bit further:

W -> J
X -> K
Y -> L
Z -> M
[ -> [
\ -> \
] -> ]
^ -> ^
_ -> _
` -> `
a -> n
b -> o
c -> p
d -> q

Answer 5

Even shorter and (perhaps) still easier to read is

char a = c < 'a' ? 'A' : 'a';
return (c - a + 13) % 26 + a;

Note that this solution, like some of the previous answers, doesn't check the input. Moreover, in Java this code returns an int, not a char, so a cast would be necessary if the method in which it is included returns a char.

As already mentioned, I also like to stress that shortest is not necessarily best. Write readable code.

Answer 6

Well, if we're going for short over readable;

return (c&~32) >= 'A' && (c&~32) <= 'Z' ? ((c&31) + 12) % 26 + (c&~31) + 1 : c;