[Jprogramming] Code golf: approximate pi

Tue Jul 23 02:13:48 UTC 2013

I don't have an SO account, so go ahead and post that. While I'm at it,
I shaved a character off the original by noting that the length of the
circle is half the diameter for even lengths. This doesn't hold for odd
lengths, so it won't help there.
c=:({&' *',&":2*+/@,%*:@#)@:>_2{.\|@j./~@i:@<:
Marshall
On Mon, Jul 22, 2013 at 10:07:57PM -0400, Dan Bron wrote:
> Oh! Nice. If you have an account on SO feel free to post it, I'll vote it
> up past my original. If you don't, I'll replace mine with yours and link to
> your message on the Forum.
>> -Dan
>> -----Original Message-----
> From: programming-bounces at forums.jsoftware.com
> [mailto:programming-bounces at forums.jsoftware.com] On Behalf Of Marshall
> Lochbaum
> Sent: Monday, July 22, 2013 9:38 PM
> To: programming at jsoftware.com
> Subject: Re: [Jprogramming] Code golf: approximate pi
>> I haven't been able to shorten your code. But here's a version which handles
> odd numbers, at the cost of only two characters:
>> c=:*:({&' *'@],&":2%(%+/@,))]>(|@j./~2&|#])@i:@<:
>> Rather than filtering by position (_2{.\]), we filter the x values by
> oddness (2&|#]).
>> Marshall
>> On Mon, Jul 22, 2013 at 07:54:21PM -0400, Dan Bron wrote:
> > There's a code golf challenge on StackOverflow [1] which asks us to 
> > generate an approximation of a circle in ASCII (i.e. using integral 
> > Cartesian
> > coordinates) and a corresponding estimation of pi.
> > 
> > For example, the 8th order circle in ASCII has 15 rows and 8 columns 
> > and gives an approximate value of pi of 3.125. The detailed 
> > specifications of input, output, and edge cases can be found at 
> > http://stackoverflow.com/questions/2440314/code-golf-day/ but the 
> > general concept is take positive integer as an input, and output the 
> > circle with its corresponding estimate of pi. Like this:
> > 
> > 	 c 8
> > 	 ******* 
> > 	 ************* 
> > 	***************
> > 	***************
> > 	***************
> > 	***************
> > 	 ************* 
> > 	 ******* 
> > 	3.125 
> > 
> > This is a code golf challenge. Most common programming languages can 
> > get it down to ~100 characters. The shortest solution, outside of J, 
> > is written in bc (the command-line calculator) and weighs in at 88
> characters.
> > 
> > Without too much effort, I put together a J solution of 47 characters 
> > (a little over half the length of the previous champion)*.
> > 
> > Uncompressed, the verb might look like this:
> > 
> > 	c =: verb define
> > 		pythag =. y > | j./~ i:y-1 NB. r^2 > x^2 + y^2
> > 		squished =. _2 {.\ pythag NB. Odd rows only
> > 		piApx =. (2 * +/ , squished) % y*y
> > 		(squished { ' *') , ": piApx
> > 	)
> > 
> > Here it is in its compressed form:
> > 
> > 	c=:*:({&' *'@],&":2%(%+/@,))_2{.\]>|@j./~@i:@<: 
> > 
> > Can you pare it down at all? Perhaps using a different approach?
> > 
> > Note also that there is extra credit available for a solution which 
> > handles odd inputs (i.e. odd numbers) appropriately, which this version
> doesn't.
> > 
> > -Dan
> > 
> > * The 47 characters includes the assignment to a name, so the function 
> > can be reused.
> > 
> > 
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