@ConorO'Brien Ok imagine we have a rectangle object. We can upcast it to a polygon, since all rectangles are polygons, this succeeds. We can also downcast it to a square, but since while squares are rectangles we don't know if this particular rectangle is a square, so it might throw an error.
@Deadcode I meant that I read the solution but couldn't see why it worked. I've gone through the algebra now to see that the division by k works. But still don't really understand it. FYI, the first part can be replaced by (?=(x((xx)*))\1*$), and then \2 instead of \3
@H.PWiz Thank you very much! That's -5 bytes. And the multiplication algorithm works because it's actually exactly like counting out the number of times the factor fits into the product. That's why it's important which factor is greater than or equal to the other one.
I would be really curious to see what kind of proof an actual mathematician would come up with that this unary regex multiplication algorithm always works.
I never got around to asking teukon this question.
@H.PWiz Okay the problem is, you're using a multiplication that only works if you have a .* before it, but you're using it on a constant. So it will find a match.
It's important that you cycle through all the possible values the product could have, starting with zero, and the smallest one that satisfies the conditions is your match.
And then you compare it against the product to see if it matches.
But that's actually not the most efficient way to do a correct-multiplication-statement matching regex.
It's just the best way to do it within the context of a larger regex, to actually calculate multiplication.
I'd really like to post it on codegolf... there's currently no question where it'd belong. Should I post the question as a typical one? Take a nonnegative integer as input, divide it by sqrt(2) and return the rounded answer. You may choose the type of rounding (floor, ceiling, nearest with round half up, nearest with round half to even, or even arbitrary or random).
Submissions could be in any language, and I could submit my regex as one of the answers to my own question.
Anonymous
@Deadcode I would recommend specifying a rounding method in the challenge. Challenges where part of the spec is "choose one" are usually not as well-received as challenges where the requirements are fully specified.
@Mego How about if I have a ranked list of rounding techniques, and require that the highest-ranked method giving an equal-length program is the one that be used. (Of course, to the best of the answerer's ability to determine.)
e.g. if ceiling results in the same program length as floor, they must use floor.
Anonymous
That would be complicated, and would probably lead to fewer answers being posted
Okay, then I'll leave it as use whichever rounding technique you choose. The only requirement is that the difference between the returned value and the precise value is always less than 1.
Should I use the sandbox?
Anonymous
4:05 AM
@Deadcode My answer to that question will always be yes, regardless of who asks it.
@Mego Am I supposed to leave a question in the sandbox when I ask it officially, or delete it from the sandbox, or move it from the sandbox?
Oh, it says right there.
Delete it.
Also, what I'm thinking I want to say is, "If your language has a built-in arbitrary precision integer type, either as part of the language or a standard library, you must use it. Otherwise, use the largest fixed-size integer type available, unsigned if possible."
@Deadcode haven't read whole context but downside with this is in JS there is a non-insignificant byte overhead when dealing with bigints along with different semantics compared to normal numbers
well that would be true in any language. The amount of overhead would vary, of course.
Anonymous
@Deadcode The usual (and default) requirement is native int size. So for C it's platform-dependent (usually 32 or 64 bits), for JS it's 53 bits (since Numbers are doubles), for Python it's arbitrary (since Python ints are arbitrary-precision), etc.
Is there a standard / common amount of time before a winning answer should be Accepted?
And for objective-winner code-golf challenges, is it more common for the Question submitter to Accept their favorite answer in the case of a tie, or Accept the highest-voted within that tie?
Trapped Knight Sequence code-golfnumber
Inspired by the very recent video The Trapped Knight - Numberphile, I came up with a challenge.
Introduction
The trapped knight sequence is a finite integer sequence of length 2016, starting from 1, and has the following construction rules:
Write a num...
Divide by the square root of two
The challenge is to implement a program or function (subsequently referred to as "program") that takes a nonnegative integer \$n\$ as input and returns \$n\over\sqrt{2}\$ as output, rounded to a nonnegative integer.
You may take your input and output in any reas...
How often does it happen that someone finds a golf optimization that would exponentially slow down their program? What's generally done in this kind of situation?
Should it take precedence as the main version of the program in that answer, or be a footnote?
@Deadcode Golfed solutions often have terrible performance. Unless stated otherwise by OP, your solution doesn't have to terminate before the Universe does.
@Deadcode You can always add a note saying something like A solution that will actually terminate before the heat death of the Universe is…
Challenge:
Given a matrix input, determine the amount of diagonals and anti-diagonals with duplicated numbers.
So if we have a matrix like this:
[[aa,ab,ac,ad,ae,af],
[ba,bb,bc,bd,be,bf],
[ca,cb,cc,cd,ce,cf],
[da,db,dc,dd,de,df]]
All diagonals and anti-diagonals would be:
[[aa],[ab,ba],[a...
I am very confused regarding the validity of the below program in c. I think it is logically incorrect but my teacher stresses it is. The code is
int a, b, c;
a=5;
b=6;
c=a>b;
printf("%d", c);
According to my teacher the output will be 0. Is it correct? I get it is zero if the condition is fals...
Brazil's first openly gay congressman decided not to take up his term this year because he's being harassed and receiving death threats. The president's answer to this (on Twitter of all places) was a series of 3 emoji and the words "Today's a good day" followed by another emoji.
@Adám that was actually the least of the problems. Since Marielle's assassination (and even before that), many left-wing leaning politicians have been threatened by the militias who they fight against (especially here in Rio, where this congressman is from).
Naturally he's been dealing with harassment ever since he began his political career because of being gay. He was already kinda famous because he was a runner-up (iirc) in one of the earliest editions of Big Brother Brasil and also the first openly gay participant in the program.
Most of that harassment came from the current president, by the way, and his lunatic followers.
@H.PWiz It is the Chinese remainder theorem. Just did the math and it works out perfectly. You only need two moduli, with a difference of 1 (guaranteeing that they're coprime).
The reason the moduli need to be the larger of the two factors and that factor plus or minus one, is that this only guarantees a unique solution <= their product – and the product of the smaller factor times itself minus one is going to be less than the desired product (unless both factors are the same, i.e. a square), so there could be an unwanted solution.
Salesforce's help documentation has to be some of the worst UI I've seen from a large company. No fewer than four scrollbars, and things are cut off unless your browser window is large enough.
This is probably why teukon was able to figure it out so fast. He's a mathematician and he would have been familiar with the math of it. I worked it out at a more imperative-programming level, thinking about it as multiplexing two numbers to do the multiplication as repeated addition with a counter.
Hey guys 1 post here sorry if this is asked somwere else but i couldnt finde it.
Like the title said i need a C code to replace the 1 row with the last row and 1 column with the last column in a matrix A [m][n].
Thanks for the help
We've got a lot of bounties offered. I don't think we'll have enough categories to cover them all. What about offering second place bounties in each category? (250? 300?) — DJMcMayhem ♦1 hour ago
@H.PWiz It is a simple proof. The algebra shows why the modulo has the value is has, i.e. with A*B=C, C-B=(A-1)*B, thus C ≡ B mod A-1, and the Chinese remainder theorem shows that the residues of the moduli A and A-1 uniquely determine the value of C within the range of 0..(A*(A-1)).
I love the Chinese remainder theorem. It shows up everywhere. Don't know why this ring is isomorphic to that field over the rational numbers? Chinese remainder theorem. Don't understand why this function has real roots equal to the function when expressed in radians? Chinese remainder theorem. Don't know the average air speed velocity of an unladen swallow? You guessed it, Chinese remainder theorem.
CMCcode-golf Given a rectangular non-jagged matrix, rotate the last row to be the first row, then rotate the last column to be the first column, shifting the rest of the elements as appropriate.
Ambigous Locations on a Grid
code-golf grid
You have a little robot with four distance sensors. It knows the layout of a room, but it has no sense of orientation other than being able to lock onto the grid orientation. You want to be able to find out where the robot is based on the readings, ...
Divide by the square root of two
The challenge is to implement a program or function (subsequently referred to as "program") that takes a nonnegative integer \$n\$ as input and returns \$n\over\sqrt{2}\$ as output, rounded to a nonnegative integer.
You may take your input and output in any reas...
Challenge:
Given a matrix input, determine the amount of diagonals and anti-diagonals with duplicated numbers.
So if we have a matrix like this:
[[aa,ab,ac,ad,ae,af],
[ba,bb,bc,bd,be,bf],
[ca,cb,cc,cd,ce,cf],
[da,db,dc,dd,de,df]]
All diagonals and anti-diagonals would be:
[[aa],[ab,ba],[a...
I am very confused regarding the validity of the below program in c. I think it is logically incorrect but my teacher stresses it is. The code is
int a, b, c;
a=5;
b=6;
c=a>b;
printf("%d", c);
According to my teacher the output will be 0. Is it correct? I get it is zero if the condition is fals...
Hey guys 1 post here sorry if this is asked somwere else but i couldnt finde it.
Like the title said i need a C code to replace the 1 row with the last row and 1 column with the last column in a matrix A [m][n].
Thanks for the help
Ambigous Locations on a Grid
code-golf grid
You have a little robot with four distance sensors. It knows the layout of a room, but it has no sense of orientation other than being able to lock onto the grid orientation. You want to be able to find out where the robot is based on the readings, ...
