Joey K Tuttle wrote:
>
> At 13:43 -0500 2009/12/07, Richard Kubina wrote:
>>..well the >: to i.1000 is silly... a slight fix:
>>
>> >./(#~ (= (|.&.":)"0)) ,*/~i.1000
>>
>>Sorry for double post, this is exciting (:
>
>
> I agree with Don that your use of &. is cute. Adding one more token (
> ~. ) to only work on unique values would speed up your algorithm by a
> factor of 4 -
>
> >./(#~ (= (|.&.":)"0)) ~. ,*/~i.1000
>
> A little different and more explicit route would be -
>
> maxpal =: 3 :
> '>./(*./zd=|.zd)#z[zd=.''0123456789''i.|:":,.z=.~.,*/~i.y'
>
> which is considerably faster. I think it is easier to parse the
> explicit verb than a generated tacit one:
>
> 13 : '>./(*./zd=|.zd)#z[zd=.''0123456789''i.|:":,.z=.~.,*/~i.y'
> ([: ('0123456789' i. [: |: [: ": ,.) [: ~. [: , [: */~ i.) ([: >./
> ([: ([: *./ ] = |.) [) # ]) [: ~. [: , [: */~ i.
>
> And the generated tacit one is a little slower than the explicit one,
> the (normalized) time comparisons are:
>
> Time Expression
> ____ _______________________
> 1 >./(#~ (= (|.&.":)"0)) ,*/~i.1000
> 0.259 >./(#~ (= (|.&.":)"0)) ~. ,*/~i.1000
> 0.026 >./(*./zd=|.zd)#z[zd=.'0123456789'i.|:":,.z=.~.,*/~i.1000
>
> ----------------------------------------------------------------------
> For information about J forums see http://www.jsoftware.com/forums.htm
>
>
The automatically generated verb that you give:
maxpal1=:([: ('0123456789' i. [: |: [: ": ,.) [: ~. [: , [: */~ i.) ([: >./
([: ([: *./ ] = |.) [) # ]) [: ~. [: , [: */~ i.
is sub-optimal since it computes z twice.
If we transform it by hand, we get:
maxpal2=:'0123456789'&i.@:|:@:":@:,.@:~.@:,@:(*/~)@:i. (*./@:(= |.)@:[
>./@:# ]) ~.@:,@:(*/~)@:i.
where now we can take out the common subexpression to get:
maxpal3=:[:('0123456789'&i.@:|:@:":@:,. (*./@:(= |.)@:[ >./@:# ])
])~.@:,@:(*/~)@:i.
maxpal 1000
906609
maxpal1 1000
906609
maxpal2 1000
906609
maxpal3 1000
906609
Timing:
6!:2 'maxpal 10000'
12.977
6!:2 'maxpal1 10000'
16.3638
6!:2 'maxpal2 10000'
14.3939
6!:2 'maxpal3 10000'
10.7871
--
View this message in context:
http://old.nabble.com/Code-review---Euler-tp26659423s24193p26686567.html
Sent from the J Programming mailing list archive at Nabble.com.
----------------------------------------------------------------------
For information about J forums see http://www.jsoftware.com/forums.htm
