Re: kombinacie :: Something smarter than us is going to emerge


node:	Re: kombinacie
template:	4
parent:	kombinacie
owner:	ziman
viewed by:
created:	14.08.2009 - 16:57:19
updated:	14.08.2009 - 16:58:39

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ABSOLUT
KYBERIA

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system:	public
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Vypocet v zoznamovej monade:

>>> import operator

>>> concat = lambda xs: reduce(operator.concat, xs, [])

>>> fm = lambda p,xs: [[]] if not xs else concat([map(lambda y: [xs[0]]+y, fm(p,xs[1:])) if b else fm(p,xs[1:]) for b in p(xs[0])])

>>> fm(lambda _: [True, False], [1,2,3,4])

[[1, 2, 3, 4], [1, 2, 3], [1, 2, 4], [1, 2], [1, 3, 4], [1, 3], [1, 4], [1], [2, 3, 4], [2, 3], [2, 4], [2], [3, 4], [3], [4], []]

Specializovanejsi postup:

>>> fm = lambda xs: [[]] if not xs else map(lambda y: [xs[0]]+y, fm(xs[1:])) + fm(xs[1:])

>>> fm([1,2,3,4])

[[1, 2, 3, 4], [1, 2, 3], [1, 2, 4], [1, 2], [1, 3, 4], [1, 3], [1, 4], [1], [2, 3, 4], [2, 3], [2, 4], [2], [3, 4], [3], [4], []]

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ziman 14.08.2009 - 17:36:34 (modif: 14.08.2009 - 17:38:02) [4K] , level: 1, UP NEW !!CONTENT CHANGED!!

Re[2]: kombinacie

este ma napada, ze by sa to dalo mierne upravit takto:

fm = lambda x: [[x[0]]+y for y in fm(x[1:])] + fm(x[1:]) if x else [[]]

co je trochu strucnejsie

0000010100063540020763990085660804857954048581510485821004858425

tak tomuto hovorim elegantne riesenie.. vdaka

este si to vyskusam (nie som na svojom pocitaci, nemam tu python), musim vidiet na vlastne oci, ze to bezchybne funguje.. :)

ale opat obdivujem moznosti, co ponuka lambda

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A inak, velmi som ti nepomohol, pretoze som ti prezradil rovno riesenie, bral som to skor ako taku zabavku pre seba.

Skus ale z neho vycitat, ako to funguje a preco, co ten zapis znamena.

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myslim, ze som to pochopil, ide viac-menej o riesenie pomocou rekurzie.. a urcite si aj sam vyskusam vyrobit tu funkciu.. ja to beriem tiez ako zabavku, hoci jej aplikaciu aj realne vyuzijem

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mimmon 14.12.2011 - 16:08:57 , level: 5, UP NEW

Re[6]: kombinacie

prvocisla

def divi(a):

  for i in range(2,int(sqrt(a))+1):

    if not a%i: return [i]+divi(a/i)

  return [a]

000001010006354002076399008566080485795404858151048582100485842504858491048585300638610006452945

Python (cpython aspon) ma defaultne dost nizky limit na rekurziu (1000), takze radsej by som sa rekurzii vyhol v pripadoch, kde na ten limit mozes narazit. To len tak mimochodom. Pripadne sa da zmenit pomocou sys.setrecursionlimit() ale neviem aky to ma dopad na performance.

edit: a tiez pouzivaj xrange namiesto range ak to pises v python 2.x; xrange vracia generator co je setrnejsie ak a) nepotrebujes celu sekvenciu b) sekvencia je fakt velka. v python 3.x uz range vracia generator

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dakujem za tip

taketo prakticke rady a usmernenia by som potreboval castejsie :)

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ziman 14.08.2009 - 21:16:34 (modif: 14.08.2009 - 21:20:33), level: 3, UP NEW !!CONTENT CHANGED!!

Re[4]: kombinacie

na to nepotrebujes lambdu :)

def fm(x): return [[x[0]]+y for y in fm(x[1:])] + fm(x[1:]) if x else [[]]

len som to tam tak nejak zo zotrvacnosti...

0000010100063540020763990085660804857954048581510485821004858334

sick :)