11
1
I am trying to golf down some C++. Is it possible to make this condition shorter?
X > 3 & X - Y > 1
(Apart from removing whitespace, of course.)
So, X is at least 4 but X >= Y + 2.
X and Y are integers in the [0,5] interval.
I have tried to find some bitwise formula but failed.
Cristy
Posted 2014-05-03T18:02:34.340
Reputation: 229
11
After brute forcing every useful combination of symbols under 9 characters, I've found there to be no smaller solution than x>3&x-y>1.
For fun here's some funky 9 character solutions the brute forcer found:
-x<~y>4>x
~y+x>2>>y
x*x-y*y>9
~y>x/~3*x
-3>>y>y-x
~y+x<<y>2
Brute forcing was done in Python, building top-down syntax trees where no child may have an operator with precedence lower than its parent according to C's rules. To cut down on possibilities I only allowed single digit literals, and no binary operator may have two constant children. I could not possibly think of any solution that would have a two digit literal, or one that builds a constant using a binary operator. Then each expression was evaluated for [0, 5] and if it matches it gets printed.
orlp
Posted 2014-05-03T18:02:34.340
Reputation: 37 067
I really like x*x-y*y>9. Perhaps you should try multi-digit constants as well? (also, parentheses) – John Dvorak – 2015-03-11T09:21:06.467
@JanDvorak me too. It expresses well the logic of "distance between x and y". I think if you plot this in a chart, it would become more obvious. – sehe – 2015-03-11T09:26:15.303
@JanDvorak I don't think parentheses can ever be a smaller solution. A smaller solution can be a max of 8 characters, of which 2 must be xy, and 2 must be the parentheses, leaving only 4 characters of logic. I'll try running the brute forcer with 2 digit constants, but I really don't think it'll give a result. – orlp – 2015-03-11T09:27:42.070
How about, x, y, a constant, a pair of parentheses and two operators? – John Dvorak – 2015-03-11T09:29:18.847
@JanDvorak Knock yourself out, (a#b)$c is the format. Out of abc two must be x and y, leaving 3 possible locations for [0-9xy], and only one flip of xy. Only interesting operators are +-*/&|^<>, so 9 possibilities. Thus total possibilities is less than 312299 < 5832. – orlp – 2015-03-11T09:42:08.153
@JanDvorak do you think you can get smaller than 7 characters? I've just written a bit of a critique. I admit I'm not a golf.SE regular, so I might not be in the target audience. I do think my answer contributes important (data) points, though – sehe – 2015-03-11T10:34:05.573
@JanDvorak No possible expressions with double digit literals. – orlp – 2015-03-11T12:07:03.920
0
In response to the (awesome) golfs by orlp:
int16_t - so there is the assumption. Probably the bit shifts would need to +16 for 32 bit ints (that's pretty much everywhere these days). This makes them a character bigger...The only "correct" way to write it, IMO is (x>3) && (x > y+1), which may be golfed down to x>3&x>y+1 (9 characters).
(You really need to take the possibility of (larger) unsigned types into consideration, especially since unsigned-ness is "contagious" in C++ expressions. I suppose "fixing" that with the appropriate static_cast<>s would kinda defeat the purpose...)
UPDATE
With the following tests I've been able to figure out which expressions actually work reliably:
#define REPORT(caption, expr) do {\
do_report(caption, [](T x, T y) -> bool { return (expr); }, #expr); } while (false)
template <typename T> struct driver {
static void run() {
std::cout << "\n" << __PRETTY_FUNCTION__ << "\n";
// the only two correct implementations:
REPORT("MASTER" , (x>3) && (x>y+1));
REPORT("GOLF" , x>3&x>y+1);
REPORT("lookup" , "000000000000000000000000111000111100"[x*6+y]-'0');
// failing sometimes:
REPORT("question", (x>3)&(x-y>1));
REPORT("orlp0" , x>3&x-y>1);
REPORT("orlp2" , ~y+x>2>>y);
REPORT("orlp3" , x*x-y*y>9);
REPORT("orlp4" , ~y>x/~3*x);
REPORT("orlp5" , -3>>y>y-x);
REPORT("orlp6" , ~y+x<<y>2);
// failing always
REPORT("orlp1" , -x<~y>4>x);
}
private:
static void do_report(std::string const& caption, bool (*f)(T,T), char const* expression) {
std::string r;
for (T x = 0; x < 6; ++x) for (T y = 0; y < 6; ++y) r += f(x, y)?'1':'0';
bool const correct = "000000000000000000000000111000111100" == r;
std::cout << (correct?"OK\t":"ERR\t") << r << "\t" << caption << "\t" << expression << "\n";
}
};
int main() {
driver<int8_t>::run();
driver<int16_t>::run();
driver<int32_t>::run();
driver<int64_t>::run();
driver<uint8_t>::run();
driver<uint16_t>::run();
driver<uint32_t>::run();
driver<uint64_t>::run();
}
Output on coliru, here for reference:
static void driver<T>::run() [with T = signed char]
OK 000000000000000000000000111000111100 MASTER (x>3) && (x>y+1)
OK 000000000000000000000000111000111100 GOLF x>3&x>y+1
OK 000000000000000000000000111000111100 lookup "000000000000000000000000111000111100"[x*6+y]-'0'
OK 000000000000000000000000111000111100 question (x>3)&(x-y>1)
OK 000000000000000000000000111000111100 orlp0 x>3&x-y>1
OK 000000000000000000000000111000111100 orlp2 ~y+x>2>>y
OK 000000000000000000000000111000111100 orlp3 x*x-y*y>9
OK 000000000000000000000000111000111100 orlp4 ~y>x/~3*x
OK 000000000000000000000000111000111100 orlp5 -3>>y>y-x
OK 000000000000000000000000111000111100 orlp6 ~y+x<<y>2
ERR 000000000000000000000000000000000000 orlp1 -x<~y>4>x
static void driver<T>::run() [with T = short int]
OK 000000000000000000000000111000111100 MASTER (x>3) && (x>y+1)
OK 000000000000000000000000111000111100 GOLF x>3&x>y+1
OK 000000000000000000000000111000111100 lookup "000000000000000000000000111000111100"[x*6+y]-'0'
OK 000000000000000000000000111000111100 question (x>3)&(x-y>1)
OK 000000000000000000000000111000111100 orlp0 x>3&x-y>1
OK 000000000000000000000000111000111100 orlp2 ~y+x>2>>y
OK 000000000000000000000000111000111100 orlp3 x*x-y*y>9
OK 000000000000000000000000111000111100 orlp4 ~y>x/~3*x
OK 000000000000000000000000111000111100 orlp5 -3>>y>y-x
OK 000000000000000000000000111000111100 orlp6 ~y+x<<y>2
ERR 000000000000000000000000000000000000 orlp1 -x<~y>4>x
static void driver<T>::run() [with T = int]
OK 000000000000000000000000111000111100 MASTER (x>3) && (x>y+1)
OK 000000000000000000000000111000111100 GOLF x>3&x>y+1
OK 000000000000000000000000111000111100 lookup "000000000000000000000000111000111100"[x*6+y]-'0'
OK 000000000000000000000000111000111100 question (x>3)&(x-y>1)
OK 000000000000000000000000111000111100 orlp0 x>3&x-y>1
OK 000000000000000000000000111000111100 orlp2 ~y+x>2>>y
OK 000000000000000000000000111000111100 orlp3 x*x-y*y>9
OK 000000000000000000000000111000111100 orlp4 ~y>x/~3*x
OK 000000000000000000000000111000111100 orlp5 -3>>y>y-x
OK 000000000000000000000000111000111100 orlp6 ~y+x<<y>2
ERR 000000000000000000000000000000000000 orlp1 -x<~y>4>x
static void driver<T>::run() [with T = long int]
OK 000000000000000000000000111000111100 MASTER (x>3) && (x>y+1)
OK 000000000000000000000000111000111100 GOLF x>3&x>y+1
OK 000000000000000000000000111000111100 lookup "000000000000000000000000111000111100"[x*6+y]-'0'
OK 000000000000000000000000111000111100 question (x>3)&(x-y>1)
OK 000000000000000000000000111000111100 orlp0 x>3&x-y>1
OK 000000000000000000000000111000111100 orlp2 ~y+x>2>>y
OK 000000000000000000000000111000111100 orlp3 x*x-y*y>9
OK 000000000000000000000000111000111100 orlp4 ~y>x/~3*x
OK 000000000000000000000000111000111100 orlp5 -3>>y>y-x
OK 000000000000000000000000111000111100 orlp6 ~y+x<<y>2
ERR 000000000000000000000000000000000000 orlp1 -x<~y>4>x
static void driver<T>::run() [with T = unsigned char]
OK 000000000000000000000000111000111100 MASTER (x>3) && (x>y+1)
OK 000000000000000000000000111000111100 GOLF x>3&x>y+1
OK 000000000000000000000000111000111100 lookup "000000000000000000000000111000111100"[x*6+y]-'0'
OK 000000000000000000000000111000111100 question (x>3)&(x-y>1)
OK 000000000000000000000000111000111100 orlp0 x>3&x-y>1
OK 000000000000000000000000111000111100 orlp2 ~y+x>2>>y
OK 000000000000000000000000111000111100 orlp3 x*x-y*y>9
OK 000000000000000000000000111000111100 orlp4 ~y>x/~3*x
OK 000000000000000000000000111000111100 orlp5 -3>>y>y-x
OK 000000000000000000000000111000111100 orlp6 ~y+x<<y>2
ERR 000000000000000000000000000000000000 orlp1 -x<~y>4>x
static void driver<T>::run() [with T = short unsigned int]
OK 000000000000000000000000111000111100 MASTER (x>3) && (x>y+1)
OK 000000000000000000000000111000111100 GOLF x>3&x>y+1
OK 000000000000000000000000111000111100 lookup "000000000000000000000000111000111100"[x*6+y]-'0'
OK 000000000000000000000000111000111100 question (x>3)&(x-y>1)
OK 000000000000000000000000111000111100 orlp0 x>3&x-y>1
OK 000000000000000000000000111000111100 orlp2 ~y+x>2>>y
OK 000000000000000000000000111000111100 orlp3 x*x-y*y>9
OK 000000000000000000000000111000111100 orlp4 ~y>x/~3*x
OK 000000000000000000000000111000111100 orlp5 -3>>y>y-x
OK 000000000000000000000000111000111100 orlp6 ~y+x<<y>2
ERR 000000000000000000000000000000000000 orlp1 -x<~y>4>x
static void driver<T>::run() [with T = unsigned int]
OK 000000000000000000000000111000111100 MASTER (x>3) && (x>y+1)
OK 000000000000000000000000111000111100 GOLF x>3&x>y+1
OK 000000000000000000000000111000111100 lookup "000000000000000000000000111000111100"[x*6+y]-'0'
ERR 000000000000000000000000111001111100 question (x>3)&(x-y>1)
ERR 000000000000000000000000111001111100 orlp0 x>3&x-y>1
ERR 111111011111001111000111111011111101 orlp2 ~y+x>2>>y
ERR 011111001111000111000011111001111100 orlp3 x*x-y*y>9
ERR 111111111111111111111111111111111111 orlp4 ~y>x/~3*x
ERR 111111011111001111000111111011111101 orlp5 -3>>y>y-x
ERR 111111011111001111000111111011111101 orlp6 ~y+x<<y>2
ERR 000000000000000000000000000000000000 orlp1 -x<~y>4>x
static void driver<T>::run() [with T = long unsigned int]
OK 000000000000000000000000111000111100 MASTER (x>3) && (x>y+1)
OK 000000000000000000000000111000111100 GOLF x>3&x>y+1
OK 000000000000000000000000111000111100 lookup "000000000000000000000000111000111100"[x*6+y]-'0'
ERR 000000000000000000000000111001111100 question (x>3)&(x-y>1)
ERR 000000000000000000000000111001111100 orlp0 x>3&x-y>1
ERR 111111011111001111000111111011111101 orlp2 ~y+x>2>>y
ERR 011111001111000111000011111001111100 orlp3 x*x-y*y>9
ERR 111111111111111111111111111111111111 orlp4 ~y>x/~3*x
ERR 111111011111001111000111111011111101 orlp5 -3>>y>y-x
ERR 111111011111001111000111111011111101 orlp6 ~y+x<<y>2
ERR 000000000000000000000000000000000000 orlp1 -x<~y>4>x
Since this about the "cost" of repeating source code elements, you might use a lookup table. You can "hide" the lookup table, so it is either
LUT[x][y]
or
LUT[x*6+y]
Of course you can be pedantic and obtuse and rename the LUT
L[x][y]
So my "version" is ... 7 characters. (Or make if a function and L(x,y) is even shorter).
Or, more importantly: correct, testable and maintainable.
sehe
Posted 2014-05-03T18:02:34.340
Reputation: 360
Added a "true" golf. No shorter than 9 characters, but the first one to be correct! – sehe – 2015-03-11T10:42:45.290
I can only match the length, but can't come up with anything shorter. My solution is
x>3+y*y/7for what it is worth (not much). – CasaDeRobison – 2015-02-24T09:24:03.420It's.... pretty short already. – Geobits – 2014-05-03T18:05:27.390
Yeah, but the problem is that I use this condition (only with variable names changed) in more places, so they add up. I think there can be a formula for this condition, noting that they are in [0,5] interval, but can't see it. – Cristy – 2014-05-03T18:06:39.110
If you use it often and don't want to type it out each time, use a function? – Geobits – 2014-05-03T18:07:37.727
I used it like 4 times, so that is 36 characters. Creating a function + calling it will be longer. – Cristy – 2014-05-03T18:08:30.707
It's generally not a good idea to use
&for logical operations. – Joe Z. – 2014-05-03T18:16:07.6801@JoeZ. For CodeGolf? Why? As long as it is working... – Cristy – 2014-05-03T18:22:12.343
1Guys, what's with the close votes? This is not a general programming question? This is about advice for code golfing. (@Cristy you may want to make that clearer in the question though, before the question does get closed and starts amassing downvotes.) – Martin Ender – 2014-05-03T19:25:38.187
@Cristy I took the liberty to do that as the close-votes keep coming in. Feel free to rephrase my edit. – Martin Ender – 2014-05-03T19:41:41.627
Oh, I assumed that all the questions on codegolf.se.com are about codegolf, lol :D – Cristy – 2014-05-03T19:56:35.037
4@Cristy yes they are, but (so far) questions asking about golfing advice are very rare whereas most questions asking for advice are indeed just general programming questions - which are off-topic. Hence, I can understand why the first reaction of people might be, "oh that's another question that actually belongs on SO", without even thinking it could be about golfing advice. I'd actually like to see more of these in the future, and maybe there'll be a tag for them some day or so, and it will be clear immediately that you know how to use this site. ;) – Martin Ender – 2014-05-03T20:23:23.970
1
@m.buettner I tend to agree that this kind of code-golf advice question is possibly a good fit for this site. Of course the tagging would need to be sorted out - perhaps [tag:advice] or something like that. Do you want to take this to meta?
– Digital Trauma – 2014-05-03T20:50:42.957@DigitalTrauma I want to and will (later tonight or tomorrow) – Martin Ender – 2014-05-03T20:53:09.743
1
@m.buettner http://meta.codegolf.stackexchange.com/questions/1470/re-evaluating-tips-and-tip-like-questions
– Doorknob – 2014-05-03T21:14:37.810(/cc @DigitalTrauma, see above comment) – Doorknob – 2014-05-03T21:14:58.363
@Doorknob yep, I'm aware of that question. Already considering whether my post will be an answer to it or a new question (referencing yours). ;) Depends on whether my actual post will be more of a question or answer I suppose. ^^ – Martin Ender – 2014-05-03T21:23:09.710
Just to be sure: When you say that “
XandYrange in the [0,5] interval.”, this means that they are floats? – Wrzlprmft – 2014-05-08T18:33:16.7734If they are integers between 0..5 inclusive, you can do the same thing with
x*x-y*y>9. It's the same amount of characters, but you may be able to find a shortcut/alternative to that approach. Just another way of looking at it. – Geobits – 2014-05-08T18:43:32.880@Wrzlprmft They are integers. – Cristy – 2014-05-09T17:54:39.580
5Use Python:
3<x>y+1– avall – 2014-05-09T22:32:45.4501I tried to prove mathematically that this cannot be improved, but didn't quite manage to :) (The general idea was that you need at least one asymmetrical operation, as well as at least one comparison operator and one number... and I just can't see a way to pull that off in C++ under 9 characters) – Tal – 2014-06-04T07:04:28.467
1Ppl, stop trying to close this topic. It's not an OT because it is about Codegolf. It isn't a programming problem to solve but to golf a problem. It is 100% valid question. – avall – 2014-06-09T07:41:52.337
I guess what you mentioned is optimal solution since there are <br>- two checks and <br>- involves two variables – Parvej Solkar – 2014-06-24T10:05:11.423
2I found a lot of solutions with Python's operator precedence, e.g.
y+3<2^x, but C's operator precedence is different. I'm betting there's a 7-char solution, just have to modify my script to deal with C operator precedence instead – Claudiu – 2014-09-15T01:17:20.4431This solution is longer, but seems interesting:
(x&4)>>(y^x&1)– Qwertiy – 2014-10-23T09:30:35.280