The phrase squished{' *' indexes the list ' *' by the (hopefully) boolean
array squished. Therefore, each 0 element in squished selects a blank and
each 1 element in squishes selects a *.
On Wed, Jul 24, 2013 at 6:50 AM, junhua guodong <[email protected]> wrote:
> Why is there a space before * in ' *'? Thanks,
>
> -----Original Message-----
> From: "Dan Bron" <[email protected]>
> Sent: 7/22/2013 7:54 PM
> To: "'J Programming'" <[email protected]>
> Subject: [Jprogramming] Code golf: approximate pi
>
> 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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