JavaScript 中最快的阶乘函数是什么? [英] What is the fastest factorial function in JavaScript?

问题描述

在 JavaScript 中寻找 factorial 函数的真正快速实现.有什么建议吗?

Looking for a really fast implementation of factorial function in JavaScript. Any suggests?

推荐答案

您可以 搜索 (1...100)！在 Wolfram|Alpha 上预先计算阶乘序列.

You can search for (1...100)! on Wolfram|Alpha to pre-calculate the factorial sequence.

前 100 个数字是:

The first 100 numbers are:

<代码> 1，2，6，24，120，720，5040，40320，362880，3628800，39916800，479001600，6227020800，87178291200，1307674368000，20922789888000，355687428096000，6402373705728000，121645100408832000，2432902008176640000，51090942171709440000，1124000727777607680000，25852016738884976640000，620448401733239439360000，15511210043330985984000000，403291461126605635584000000，10888869450418352160768000000，304888344611713860501504000000，8841761993739701954543616000000，265252859812191058636308480000000，8222838654177922817725562880000000，263130836933693530167218012160000000，8683317618811886495518194401280000000，295232799039604140847618609643520000000，10333147966386144929666651337523200000000，371993326789901217467999448150835200000000，13763753091226345046315979581580902400000000，523022617466601111760007224100074291200000000，20397882081197443358640281739902897356800000000，815915283247897734345611269596115894272000000000，33452526613163807108170062053440751665152000000000，1405006117752879898543142606244511569936384000000000，60415263063373835637355132068513997507264512000000000，2658271574788448768043625811014615890319638528000000000，119622220865480194561963161495657715064383733760000000000，5502622159812088949850305428800254892961651752960000000000，258623241511168180642964355153611979969197632389120000000000，12413915592536072670862289047373375038521486354677760000000000，608281864034267560872252163321295376887552831379210240000000000，30414093201713378043612608166064768844377641568960512000000000000，1551118753287382280224243016469303211063259720016986112000000000000，80658175170943878571660636856403766975289505440883277824000000000000，4274883284060025564298013753389399649690343788366813724672000000000000，230843697339241380472092742683027581083278564571807941132288000000000000，12696403353658275925965100847566516959580321051449436762275840000000000000，710998587804863451854045647463724949736497978881168458687447040000000000000，40526919504877216755680601905432322134980384796226602145184481280000000000000，2350561331282878571829474910515074683828862318181142924420699914240000000000000，138683118545689835737939019720389406345902876772687432540821294940160000000000000，8320987112741390144276341183223364380754172606361245952449277696409600000000000000，507580213877224798800856812176625227226004528988036003099405939480985600000000000000，31469973260387937525653122354950764088012280797258232192163168247821107200000000000000，1982608315404440064116146708361898137544773690227268628106279599612729753600000000000000，126886932185884164103433389335161480802865516174545192198801894375214704230400000000000000，8247650592082470666723170306785496252186258551345437492922123134388955774976000000000000000，544344939077443064003729240247842752644293064388798874532860126869671081148416000000000000000，36471110918188685288249859096605464427167635314049524593701628500267962436943872000000000000000，2480035542436830599600990418569171581047399201355367672371710738018221445712183296000000000000000，171122452428141311372468338881272839092270544893520369393648040923257279754140647424000000000000000，11978571669969891796072783721689098736458938142546425857555362864628009582789845319680000000000000000，850478588567862317521167644239926010288584608120796235886430763388588680378079017697280000000000000000，61234458376886086861524070385274672740778091784697328983823014963978384987221689274204160000000000000000，4470115461512684340891257138125051110076800700282905015819080092370422104067183317016903680000000000000000，330788544151938641225953028221253782145683251820934971170611926835411235700971565459250872320000000000000000，24809140811395398091946477116594033660926243886570122837795894512655842677572867409443815424000000000000000000，1885494701666050254987932260861146558230394535379329335672487982961844043495537923117729972224000000000000000000，145183092028285869634070784086308284983740379224208358846781574688061991349156420080065207861248000000000000000000，11324281178206297831457521158732046228731749579488251990048962825668835325234200766245086213177344000000000000000000，894618213078297528685144171539831652069808216779571907213868063227837990693501860533361810841010176000000000000000000，71569457046263802294811533723186532165584657342365752577109445058227039255480148842668944867280814080000000000000000000，5797126020747367985879734231578109105412357244731625958745865049716390179693892056256184534249745940480000000000000000000，475364333701284174842138206989404946643813294067993328617160934076743994734899148613007131808479167119360000000000000000000，39455239697206586511897471180120610571436503407643446275224357528369751562996629334879591940103770870906880000000000000000000，3314240134565353266999387579130131288000666286242049487118846032383059131291716864129885722968716753156177920000000000000000000，281710411438055027694947944226061159480056634330574206405101912752560026159795933451040286452340924018275123200000000000000000000，2422709538367273238176552320344125971528487055242938175083876449672016224974245027678946463490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如果你仍然想自己计算值，你可以使用memoization:

If you still want to calculate the values yourself, you can use memoization:

var f = [];
function factorial (n) {
  if (n == 0 || n == 1)
    return 1;
  if (f[n] > 0)
    return f[n];
  return f[n] = factorial(n-1) * n;
}

21.08.2014

解决方案 2

我认为添加一个使用大数的懒惰 迭代 阶乘函数的工作示例会很有用> 以记忆和缓存作为比较，得到精确结果

21.08.2014

Solution 2

I thought it would be useful to add a working example of lazy iterative factorial function that uses big numbers to get exact result with memoization and cache as comparison

var f = [new BigNumber("1"), new BigNumber("1")];
var i = 2;
function factorial(n)
{
  if (typeof f[n] != 'undefined')
    return f[n];
  var result = f[i-1];
  for (; i <= n; i++)
      f[i] = result = result.multiply(i.toString());
  return result;
}
var cache = 100;
// Due to memoization, following line will cache first 100 elements.
factorial(cache);

我假设您会使用某种闭包限制变量名称的可见性.

I assume you would use some kind of closure to limit variable name visibility.

参考:BigNumber沙盒:JsFiddle

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