Talk:Dutch national flag problem: Difference between revisions

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:That's a low probability event for any reasonably sized collection of balls, so I did it manually in the example. If you want it automatic, replacing ? with (3||.@/:)^:(-:/:~)@:? will work unless the user tries to generate a selection of only one random ball. [I fussed with that one a bit -- the issue behind my fussing was that I wanted a single correction step for all the improbable things that could go wrong in a random sort.] --[[User:Rdm|Rdm]] 00:58, 2 July 2012 (UTC)
:That's a low probability event for any reasonably sized collection of balls, so I did it manually in the example. If you want it automatic, replacing ? with (3||.@/:)^:(-:/:~)@:? will work unless the user tries to generate a selection of only one random ball. [I fussed with that one a bit -- the issue behind my fussing was that I wanted a single correction step for all the improbable things that could go wrong in a random sort.] --[[User:Rdm|Rdm]] 00:58, 2 July 2012 (UTC)

::Hi, The Python is set up to generate a randomized, random sample of from one to five balls of each colour so it only has to check that the balls returned are not ordered. I don't read J code but I guess if you have the possibility of generating zero balls of a colour then the check would have to be for more? --[[User:Paddy3118|Paddy3118]] 06:29, 2 July 2012 (UTC)

Revision as of 06:29, 2 July 2012

Flag request

This task needs a picture of the Dutch national flag. --Paddy3118 09:34, 1 July 2012 (UTC)

http://en.wikipedia.org/wiki/Netherlands Fwend 06:04, 2 July 2012 (UTC)

Algorithms

I kinda ducked the issue of optimized algorithms in favour of giving an answer in keeping with how things would be done idiomatically in a language. This shouldn't stop those who want to give famous algorithms as well though. --Paddy3118 09:34, 1 July 2012 (UTC)

That's completely backwards. Making a Dutch flag isn't an idiomatic thing to do no matter what language you use, and the Python and J examples' using built-in sort completely missed the point. What's interesting about the problem is that, if you know sorting the array only involves comparing a samll set of values (3 in this case), you can have an O(n) method instead of O(n log(n)) as with a standard sort. Using an "idiomatic", non-specific method here makes no sense: there are plenty other sorting tasks on RC you can go idiomaticize with, why make yet another one?
BTW, the J comment about bin sort (counting sort) isn't entirely correct: two elements may compare equal for this sorting purpose, but it doesn't mean they are necessarily identical. That is, balls with the same color may still be distinguishable from each other, and the sort routine shouldn't automatically assume otherwise. --Ledrug 02:57, 2 July 2012 (UTC)

"ensuring that they are not in the order of the Dutch national flag"

Please ensure that entries check for this too. (J language?). --Paddy3118 22:01, 1 July 2012 (UTC)

That's a low probability event for any reasonably sized collection of balls, so I did it manually in the example. If you want it automatic, replacing ? with (3||.@/:)^:(-:/:~)@:? will work unless the user tries to generate a selection of only one random ball. [I fussed with that one a bit -- the issue behind my fussing was that I wanted a single correction step for all the improbable things that could go wrong in a random sort.] --Rdm 00:58, 2 July 2012 (UTC)
Hi, The Python is set up to generate a randomized, random sample of from one to five balls of each colour so it only has to check that the balls returned are not ordered. I don't read J code but I guess if you have the possibility of generating zero balls of a colour then the check would have to be for more? --Paddy3118 06:29, 2 July 2012 (UTC)
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