Hello, fede s!
I'm guessing, unclipping a range (which is a small tuple) produces a huge array of integers.
It feels like In this algorithm you don't need any arrays at all, a simple iteration would suffice. Plus, you don't need to check all the numbers with prime?, only the odd ones, so unlcip is doubly unfit here as the propulsion engine.
The idea of doing the special range-unclip is fine. Although the current implementation never ends producing the "first" elements, even after the range is exhausted. This is due to the possibility of having ranges with negative step slot, as in `5 -5 [a,b]`. The regular `unclip` on the other hand, throws an error when applied to an empty sequence.
I've looked at the code, and I don't see a way to override the word unclip to work on ranges in the more optimal way that you suggest. Maybe some specialized words like range-unclip could be added to math.ranges?
23.01.2017, 02:24, "fede s" <elfeder...@yahoo.com.ar>:
Hi, I noticed this Q in StackExchange http://codereview.stackexchange.com/questions/153288/codewars-gap-in-primes
and attempted a (naive) solution for the problem:: next-prime ( range -- rest prime? )
dup empty?
[ f ]
[ unclip dup prime?
[ drop next-prime ] unless
] if ; recursive
:: check-gap ( gap prev rest last -- g p r l ? )
gap prev rest last
prev last - gap = ;
: (primes-gap) ( gap range last -- n1? n2? )
swap next-prime dup
[ check-gap
[ nip rot drop ]
[ [ drop ] 2dip (primes-gap) ]
if ]
[ 4 ndrop f f ] if ; recursive
: primes-gap ( gap from to -- n1? n2? )
[a,b] next-prime over
[ (primes-gap) ]
[ 3drop f f ] if ;For that version,[ 8 3,000,000 4,000,000 primes-gap [ . ] bi@ ] timegave 59 seconds on my system, most spent on unclip.I changed:: range-unclip ( r -- r' 1st )
[ first 1 + ] [ last [a,b] ] [ first ] tri ;
: next-prime ( range -- rest prime? )
dup empty?
[ f ]
[ range-unclip dup prime?
[ drop next-prime ] unless
] if ; recursivewhich gave only "Running time: 0.000342938 seconds"Factor 0.98 x86.64 (1777, heads/master-ed29fbd93f, Mon Aug 8 20:45:47 2016)
[Microsoft Visual C++ 190023506] on windows 7I know there have been some changes since then, and that I'm probably doing things in a very sub-optimal way, but thought that there may still be something of value here.
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Александр
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