javascript - node.js:嵌套for循环，字符串操作性能惨淡

Question

我写了一个脚本来从上到下而不是从左到右读取一个大字符串。当我运行代码时，我的 CPU 的一个核心卡在 @100% 上，并且代码永远不会完成。如果我取消对 console.log 的注释，它会越来越慢地吐出字母，并将所有 8 个内核固定在 @100%，内存使用率会缓慢上升，直到用完我系统上的所有 8GB，然后它会因 OOM 错误而崩溃。我显然做错了什么。

var haystack = 'SRASBPETHWTWHDZVPOAECJHGNXHRKZXRBMSDYGZGNZBBCOKVPPJKKAQECOLGBFIIKTPVSROCCWWGRWDEQTNFSKEDNFBFKWVEELVTBULWROMGTXSASKCTFJQFDOGRNMZEBLFSCFAFWXZVRGFAZHERUTMOETZZRYNUHSRTHEYIVQDXFNWDDSLSSGPFOMYRHBGKONPIWDTZUBBRAJZGBVUGMVZZTPRAXMLZSXYELKJZWXUYUQIUGGHISZHIGSUQHGHTICVWIJVXMUXOQHPDESKSPRJHQVVTRTNQEVUWKGGQDURAXZWTMYUYIISIOXLTHCISFFSNHZMCGEWMOWCHRQKYNDTDLFWERZLEPRLTNZSPFEDCDESQVMLWMXGCXPMSPTJGSXTXINFADZTBUNDIQWOAIGFKQAJWHINHMZCZVMTJJWGTSGGOIBOZCJGVURJETNXSXWEDUNJPVLPZTDIMSIZGQUJALJYWVLRDYDRWVHZNUNKOLAUPTBMKUNFQYLVQKOQIPPWVNDXENRCVABOTNEKKJPURYNAWAGIZFEHYQMOFICBCQKELTMUYVQPYPZKVBYPTLXRLMYEXGAPRCWDJHQASDQHRGSTIYGMEAWOBLFPSDBGGXFBGIARMGLYOFCZXILLFLCVKCKCXYBTKIYRHLPWXBNGLJYVIZHWPIQSQLHURYRRTBTUBYRMMEQULVVJFKRRZTZVOIKNXPIICBQGFPTETWVPVUKEQOVTCOUARDTAVZFSZWBSTWTQEGLIDKUVMTFRXHOWPPJHCEWMTHJRKXENFENKDMPEYVNEMQRDBGZDIBVYCCFLFMFPSXHHADOZWMMOJKQSYNAPOKLUPSALZVKPKVBRIAFOXSECFCULWPFNPKFGIBPAUEXEOHLTRWTLJMHEMIXSVZVRYZQXCUGNZGDSLXJSROSBAIWPKQGICVKSMAVUHZPIQHDQGLSMJUQYYAZQSVORXLRNMEOYUFAKGKHJFKQPBYKDSLYHKLCEWAQINPRGOGVCQBAKTVDZZNRSIKZVSRMFCDJSANSGNQZPPEZSIZCSQCPMIRBKJZFKVRVVNOLDSYGFLMNJHCGUZDRVHTLSJMCHZCQJUURVMEFABDKQEFYXYZEQUOLEOZWXDXXOXIFPLTFBGTKYTBVSSTJESKVIMHJSUDVKRKOJYOGWIXLODESHRMPYBWKRPFEUGIYXXGHDVYXPUBVSQPHRUSSCQDHAXMJNUNSFGHZANXDFFXDETLXVAUAPOCASOTONXBXIYFMSMUUPFGMYKWVFGTTQFSNUDFTIRWSVVEQHPVFRYPLGPGIEUMSSFONCONOPHSDWGFBIGPEKQBRPZWYLZLKCMWFOKLNQBYJREVFRLWFBDVIVIIVZUTQZOLDSNDUISKYGJTIGWYUQBXXTAPQMKULPXGCYFMZLNQDAWOBWOVTKXOABKZRWAZUDYYTYNDQAEJHEDPOYUANKWMUATXGCRRGEKDVTIGTFLQHQVFJBRIFKYLHDJUXLAMVELRZPNBSEBQUVHARMKVCLLDHHYYQNTXFIMFKRIMTJUEJOWIEIETZDADSGNJFDGGWKRJUXQXXKLOUSYMCTHLYIXSICFCRHFCXUSFOMCVSVYIIMCNEGHRMCZKWXPHFAMCTCBEBHQOBDXHAYNSVVZWAGTEIMVWRCCPNCCQGUWXIGCPZERUVJRQIZQYSMAUNHCVNROCDFORLNOWTLVTHADALVCOISZDFKNFMXQBMVUMFDFKDGNRQKZPXDJNZODBXFUAGEPCEQSLGAOSQZUHJXEQFTRLAWZUUROTADFEXJBGJCOPLRNLLHVTNPNPHJDYWEGBKVOZOFDYMYMHUNDMLIZOCLODMRBZORXZVTUAIDXZIGOLLMGUJLSOHSVDFEMDTXEUMIOITNSXVNXUWMNPFITZXAJBKUVMNLUOONUDQSWYUCZOZXOXAFRCWVMMBLFCPPHFTLEKHXQNWYMQYDLGHTSSGDCFIRSMVTJFKPLVLBWIFWBJQTKXBIMLRTGNABJDXWIEFLVCDLQTSWURMBASDXNXHBQTEBCUTGWVTHXDHRJYZZKNQEBPXRYMWAXEGRSRUCQHYIOVOYJUXPANVEAJEUKKYAWEZSPZYCQPPWXVNNPHIVSHSSYVJLUNDXAFPCXLOOTRYVLVGNIQVPZLBXAPWQGSCCXINWFTIVFGLMUTPRWQFJORMQYYIUUJZRLLFXATWFRCQDKDIFXZHCWJGYEROPRQTJGJJSTRRKAMAGGMZKKOPXYKUSNZVVHHNRAGAGWXZOIYKVMAQJELXWGUEWMTSJMOEZRUEGUBZELODZNCDASJZGOTXYZGVTVMRTVVSWHFEFVUJPCCGEJXWYYLBVZGIGCHRNQOEDELTDIUZPAGGJYPCEEKZNQSMDKNMRZFVBPLIRBFCCVLUGCVPLOPCWDZJZAMKFKRLXTKQJIZSNAQFUXMCLXPTBKNNWWKKBVLYQPFHVEHGXQEHPOWRIIWXGKVBFMMDOJNFMCCNWTALOTLCMFKXKGIKYHQIOUJOAIXEFIMWMKCTABKRCVTAFDLWIQFDUEYDOBFJOKXBKIIBCVIVILAWTFXHLUVTMGQEJEVKBAVMITJPVRGRCDSFLPXRFWGAJLGMSPAOUVMDUBXYWEOVMDNUOIMXGEVNKCALLWPPMNNMFOVTZOAPSDJFZECSDIHKXCYJCAGYKLPOWFTVSRDSBSGGWDNFSTRZQYKMOUDNTRGXFKJBLOECLUJQGRQWGUETMKOGUWCAHDHGGCBSWXTXMLJMJFJTKURTTCXNOOEBYYUVKPWXSNUKVCZOXJOMXXCLTZWBUDYMEJNTIPBTWJKJJLYQFGYRGYFUCTAICLKBYEHONSPSMXLLMZCMJQVOGKEZOYBDJIUHAFGCEIAPXAQVGSBIJVUDHTWPPEKMWWFEUCAQWFRHLCFTLPXVJNKFCTEXGKPZXQXOBKPDWOAFOZTBYGDVFAJXMQOHAPTLSNLKJIGZRFSBGMQBNBAHELRDEWUEWQVKVYZBPGQVOWYKZEGLJRLYHBETRZTEWBTGJBRUTBKNDGEAQEUTLZZSAMCMMVJWBPDKOSGPLVUKPZAQGJDKUIIPCVBOIBCXRAAANQSCBBYQNXRTCRNHJGMRYICLHDBXVXEGBFAEXOAABYDXFQTKPXVMQPHXLTXCVMLXDJPULJNOGVZFMYIRBFIEESIEJDBLYPARQERLKUEHYUGJIRKVQEFZLQUQXSKRNBZURWPLZSTPXISSJLUFZSMFXZIVESRSKEDNJEPGVPUBHLGWTKISYYJVQHXPHJDWDWQMAQWTZIBKCHEAETDYBJETTGZYHUURVERLLSCKUHSJMOAXTRYGKDXGISNNAHVQTEZKRKWAMMHAJGEJZOWZNEIZLZSSGLDGHXNEJPUBPPXNLJCKBFYDGXUPXITFATASDFNSHKWNZMQGXBBOSHEWBOWWCFKDCWVKWOTKMNEGJNOPURJJWAFPQOLNGBMAUCITMGZBOQIEUJEIOSNSMYQJTGVPFGXWCCCKDRRVDIHDYCTQHESHCTUUSSVQWMWTAOKIJALBPMGBEXZQFRIKAQVWBUXUNKBYMYSEXBNZHFHUSFGSKRQYZVKTALOHBMXSGHRUDUYSSMWFMPMMWFXCPISMWXIFEQSWTQQKUMZGOANSOASHGJBEKWLJBXENHHBWQQUCRQYNAATEWLTESGXPCWYFVQGGXTTPIBWSYRXBQGDXJMZFQRYDPKFPNYRQEFGFSZBGZRDVLHSYXTRTXFOIQIYBPFEXQDXBEPJNDPPBICIRTBBTLQUALXYUWPUDBVMJSOJPNEGIWXGCBFDZZSKWNAUIAXOVJJWULADOMBTGOTCIAYLIAGYTVVBZVVMYBWAJYQYCTNHUXYINPLAEIJCECYYBFIMUXXDGRKJADAFWWQKVSKLWKGPJPFZDCWNIHLERAIXHDIIIMDQPFTZVZTWYXYCUOCFFEYPBZRTSCPUQMWXGZVYCKTEVNJPBDUBXIUSUOOGGYGRTGAZTYRCGBKJFGXBRMDQGZXIGZDJCHWFORQKJJGUJTRIGIKOBYSRTIOUIAZWVHAWISDDWTICHGVEHSUTDFTGBIJUMXLNHLVXBOFPCEUOWQRDIELVYBAOAWLRCBJVKJCXYPJPGIJGNGJYUVFDNDCDBQXQMRYLIHDKYQHGBWBZOAOXPMALQZEWAAHGMSLSROAJPLGSIKFUSYRDJPQCOOQJTJVNPLIHJECIFUHIIEZYMJCQTCKUHSCJMUVDEZIMFEGOMRHVUVIVGMBERRPLGKWWOPLKRQIWJRZBYOSXROTLBUDGLWGKKWANWWIWJNQDCVOBSIPNXJEHKNUHSXCXDCCRSNBYZVXBUOAETHRQYYVQGLXWBWXYDRBFSBCNOSJHGTNSCIAXPCLOACAQGCBTXZGTCIDNGLAZCWXIFWKDYJWBKXDEUJZPQRLWASIKLSLFMERFKPXQYQFIRYHHUXSCWVLQZGSMLZUYOAFCUHMJIVDOEBHDKZYUDADMCHXQYIKUMKAPRPWSGDMNAGCSOOVPSCSWCENPBOCCJQXPBBDEHHVUVTFSLHGTKHASWGOUUQEDZYJOXUXELQAMKVNGAAJXMAHKARSLPRZGTDBKPRCXYHWWHWRRXXPRFKMJJNEYGHTMWCTNBQRCUAJPPPLPNJETEYDBRMLEIKLKGLJMUBPRLWIFEOOQCBGNOVMLMTZGYCGMSLCTKBVHJGUZLGYUJYXONOPRHMJEAHICJRUXILJAGNHHJXSLJTVMGGRNVKTDOJVHHXWZVJIEJCPPVKAVHWPCNBZTIMNVYGAKBJIGBNMLRAYUAHKJWCOISZHMGONXQAXWJZVQOGQUGAKJEXUNLTCDYRQWDGGOUUUUHWPRASTBFMSYGROSNLXLENLVETJKKSOLSMHVEUQRLJUDAMKJLWECCIHTUSPPTVXUVZZVDUVPVWNQUPLIHVDPUQVUIIGIYCFUANGHNOWQMSOQOMHLQNIKVQBGOQHHZFVCLPIYOXHIAXDLRZJGXAIJYNLVXEIAAIZXCUITPLABHDPJYZEOACHCRYUZNYNHPJPOPPGEKXJAAZLGPXJSNHNSQSPJRXZGYGSNDUWNJCQNPLJJGKIBUXGSPGUXZAWHYBWCDSQPWVTBCVDQRDXMXBMDVRXLPHGUFSTQPXOLOFIZKFDLJSUUUXCINQOYFULWDNUZCRJIOSRMOWVMMHNYNFBUKYXEFLIPBFEDPFJGHFXQYVUZBUNUJDLSWYREVCKMVQQVAATSRNUOSNABSMXRFVVMVTXITIYWUKTCDNZPYUGPPQOQRPDFMVUXMTKNZQWOJHWELRFYDFKTBGVVSZNBTDNPBFHAKKUFHZVUXRARYEKWUCYQXLIWONVNBYXNAQZBTVGWIDGTAWFBRMRVVKYAXJOTYYSQXZAJEOWWCOJXLBWSXGODJSUEOMYXHPUEPDYLWYJNDISRWYYFAGYMVSXPTGTTVWTFBSTFMFCYRLFISMGKAZVQBSNISILDCSLUGVWBBKWAXOPTHPJQFBTONDUMCCNEDSRBYOCIAMTLBAVESZQEAHGNFADENFWGWIGAQTOCSNXNSZNEVJMHVENBGUOOMMGCBGJBCPQPYMBHDKJPQDBLAMLLSGUEEFLNGNZJFQFZKONNDHXIUJDMBUNOVWSFBBJWRHIJSTMSQNSFPDJAXRARKGEDQDHWGZQWZRWPLWAUPUIGUXPAXHIKPDJLCQOMHRYRLJYOCSNAWRNCHSXHJTKNGMHYOHRFIYQJFSPJOMYBUPHUQJRWNQEESRWPGJKHZRNDZBQIQBNFSIAVIBDEWWSDRATKVZPBTTHJYASFTUCIIHZQTXEOTLJSVTZQWALTTBGQLPFSYITRVWMKCJOZWONQSZTPDLXESINYENYTAZYPVZPDBYGFDGEZTJPZVZDHTRKOTGZELUGEWSMYZFOSQEZNNSCVKWXCKBDDRMWFWUBJJHTVQVPARGEFMXCCKQLCOABKJYOKUPJYQNMKNDBNROJDPUANZUTBZRKPCOFJHKHJQWQZMNFOLTJVODPWFPJOEYBLPIOIWFQOETPAAZEHMYSNMSSFSTIWOZRTGGXHDKJPOKCDUCFOZJNQAUUZJONRAOJHVPQDMUHNFRBHECDFCAOLXXQBDEPIZWQHMONFDLDQDAHAZRHGJTXVUPDPZVNHJHSGBPMVFVAHYUYKRPQVSTNSQXEBMSSKJBYQKBXWSNAQZJSYPQDCRFORMTTBVWUBPYIXLLMZEOMAELSCBIMRASXWFFFFZDHEUDIRZKJMNNENEARMVLNGYGJMCAOWYICCTRIQUJAWWLAPFTBJGHHEHBVQJNIDKAGMPOLTZIKEEBQTQHFVDIAHJEZMIFWPMXTEHJQKGMHMMYPYQCARDOZERLTHGYWWJJEILSYLISWVPRSCIUXVXKSQWLKTRCWUURCLGXYQQXWQVOWXTLURZIKQRJXTPNWRNQAYMIMMUXCTZREGGHFXMMAAHZZMQIEQGBHORJGAAZAJNZIDKKXZIRRTUASAEOBPBWYDUCUILWFEUMSBCPWWMNDCEFNSDJBGVDYUOUPPLEMTQLOLVXLPFNMYNCTSSIJRLQDOWSUEREYCVPKJVBTAVKEANLCJVZHRUIOEWBCUYDLEYYDLYEYYMOUTROZIGJRHRNLISBLUGUNLZZLNHIWTDNGRLAVPOLOYSMTTLLPKDLQWNSXMIDXBHAXYEMRPYONJVJLYPFLMLOSLWTRMSHLYMSRJHXKXRGWGAIXBUCWRXCGEUWYUIUSQQPWKMHHSBDFSYZKOSQZXXAVXXXJKFCNIGXEQZNBBKEKCQOWQGQHTUIPEYUFJARTKKFHDOUHLHUZZFXLWHIOOIGKNPAXEXDNWIUQSOSBHDEQLKPLIRUQMUBHSQIGUNJSBWHLBFSUOTNJZWQDDXETAQNDYADEIGPJEBVGIDGLVDMIECXNUIELRZAUFRBSMNPOGJHHCDAVVKIYEOWLLAVCUZOCBDKPAPCUVHWXUQSUASGIBQAOROBZLGTAMIHSHOWXPQBVFCOSNQLMFGEZAZRXTIHWDWXATHYUAIDPSGBPUIVVROEXXUHHVCCCMNXFGAQIJNNVZHBEWULPGLYJHLRBFGPPJCAIAFKALYQDWBFGDYRCOQGXZLVLSMMDXEKDCMQIQBQVRGVHTYUZTHGATYRZVIGUMKADPIGSIFJZCKKJHEONIKRXKOPXAGMWBMHVPVPDWRADGMTVERKRWSSVLVFIJGMUBZTRSPNGDLFRBXGMHNEOJCMPFOAPWEPLGRABYLLXDLTERRBKDBVYGQNDYYNCHLWDWWYLLVQBOVIHFJLFVTMKDVINYKKERJKSCZTZEKQSFOSMPNVGSNQSQNDAVQJNNLQHJLBTXPZBXFYRRACYWMCKFORKWGNJCLFIXCIQSPWUWTRLJSICZVKZDAIQTURXNBGDLIREHDLDUCDNDXNSHRCLQLATVPHOZRTIXXIQYEJSARNKOOYIIFVLEGISMMEQNCMAKQLXRQRNEKMGFLCNCJWCTRDMEIFCZVJGTLGWDSTBSEUKVWEIHOHMSZKXUCCVHACKLKQJQSXKUJXPTSHKYRMUADWABQSVKIPFRPTDASYVGJXXMSHFNGRDXIQFGCUGHLKOWXPJETKDWUZHZFKEDYTKZEUUQDIJMWKYUVDYZPTWSHNJDBLZMNOTKGCWFRASJBPQYPTAKPDBFPFLZCEPKPTHTQAQVMMFXUUNEGOJOYRCSBIZZPEREIYMQYMBJIDTYCJAJVIQGHLHVYVLFXRJJWEJJEGVJOYCBVQEVXKEDKLRFSOMXWEKBCHEMLCIVTZXXTJOXHPZAIMBTJBHVSOGNWZBRFABAINEEBPWNYSBENBURPTRCAYWKCQCNZXWKRWVLVTHJWSOBEWANCJSLRWZOBPNITSTYNTVJJZNCNSPCFDQQNAMMQPVPQWTBPSAMWZECDXXCKBBEQKSKLALCZRZCNFDYOXEAYHHKRNF';

for ( var n = 0; n < 64; i += 1) {
    for ( var i = n; i < 124*64;  i += 64) {
        //console.log(haystack[i]);
        var vertical = vertical + i;
    }
}

console.log(vertical);

但是什么？我对这个大字符串和同样大的数组进行了其他 (indexOf) 操作，性能还不错。这个嵌套的 for 循环是不是一件令人讨厌的工作？应该怎么写？

Answer 1

这与字符串无关，您甚至没有访问它。

您搞砸了索引变量，循环永远不会终止。您从未在任何地方尝试增加 n，因此它永远位于 0。