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DOUG LLOYD: Kama wameweza kuona
video juu ya kujirudia,

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mchakato mzima anaweza kuwa
walionekana kidogo kichawi.

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Jinsi gani kazi?

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Jinsi gani kazi kujua kwamba wao
haja ya kusubiri na kusubiri kwa thamani mwingine

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kurudi kutoka kazi mbalimbali
piga ili kupata matokeo tunataka?

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>> Naam, sababu hii kazi ni kwa sababu
ya kitu inayojulikana kama wito stack.

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Wakati wewe piga kazi,
mfumo unaweka kando nafasi katika kumbukumbu

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kwa kazi ambayo kwa kufanya kazi yake.

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Na tunatoa wito chunks ya kumbukumbu kwamba hawa
ni kuwa zilizotengwa kwa ajili ya kila kazi

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piga sura stack au sura kazi.

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Na kama unaweza kutarajia,
muafaka haya mkusanyiko

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kuishi juu ya stack sehemu ya kumbukumbu.

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>> Kazi zaidi ya moja stack frame
unaweza kuwepo katika kumbukumbu kwa wakati huo.

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Kama kuu wito kazi hoja,
na hoja wito mwelekeo,

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kazi zote tatu na muafaka wazi.

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Lakini hawana wote wana muafaka kazi.

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Muafaka haya ni kupangwa katika stack.

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Na sura kutoka
hivi karibuni wito

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kazi ni daima juu ya stack.

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Na kwamba daima ni sura hai.

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Kuna tu kwa kweli milele moja
kazi hiyo ni kazi kwa wakati.

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Ni moja juu ya stack.

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>> Wakati kazi wito mwingine
kazi, ni aina ya mashinikizo ya kunyamaza.

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Ni aina ya ni juu ya umiliki, kusubiri.

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Na sura nyingine stack ni kusukuma
kwenye stack juu yake.

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Na kwamba inakuwa sura hai.

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Na sura mara moja
chini inahitaji kusubiri

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mpaka ni tena sura hai
kabla ya kuanza kazi yake.

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Wakati kazi ni
kamili na ni kosa,

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sura yake ni popped mbali stack.

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Hiyo ni istilahi.

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Na sura mara moja
chini yake, kama mimi tu alisema,

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inakuwa mpya kazi sura.

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>> Na kama ni wito kazi nyingine,
itakuja kutulia tena.

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Stack frame kwamba kazi mpya mapenzi
kusukuma kwenye kilele cha stack.

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Ni itabidi kufanya kazi yake.

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Ni inaweza pop nyuma mbali.

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Na kazi nyingine
chini inaweza kuendelea tena.

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>> Basi hebu kwenda kwa njia hii tena, kuangalia
katika wazo la kazi factorial

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kwamba sisi inavyoelezwa katika
kujirudia video kuona

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hasa jinsi uchawi nyuma ya hii
mchakato kujirudia unafanyika.

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Hivyo hii ni faili yetu yote, sawa?

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Sisi inavyoelezwa mbili
functions-- kuu na ukweli.

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Na kama sisi kutarajia,
C mpango wowote ni kwenda

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kuanza saa mstari wa kwanza wa kuu.

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>> Hivyo sisi kujenga mpya stack frame kwa kuu.

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Na ni kwenda kuanza mbio.

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Wito kuu printf.

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Na printf ni kwenda
magazeti nje factorial ya 5.

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Naam, ni hajui
nini factorial ya 5 ni,

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na hivyo wito huu tayari
kutegemea mwingine wito kazi.

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Hivyo kuu ni kwenda kutulia pale pale.

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Mimi nina gonna kuondoka zake
mshale haki pale, rangi

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ni alama sawa kama
stack sura juu ya haki,

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zinaonyesha kwamba kuu ni kwenda kufungia
hapa wakati factorial ya 5 inaitwa.

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>> Hivyo factorial ya 5 inaitwa.

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Na ni kwenda kuanza saa sana
mwanzo wa kazi factorial.

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Ni anauliza swali mimi sawa na 1?

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Ni 5 sawa na 1?

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Naam, hapana.

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Hivyo ni kwenda kwenda chini kwa
mwingine sehemu, kurudi n mara

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factorial ya n bala 1.

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Naam, OK.

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>> Hivyo sasa, factorial ya 5 ni
kutegemea mwingine wito

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kwa factorial, kupita
katika 4 kama parameter.

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Na hivyo factorial ya
5 sura, kwamba sura nyekundu,

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ni kwenda kufungia pale pale
wakati huo mstari nimekuwa unahitajika

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na kusubiri kwa factorial ya 4 ya kumaliza
nini mahitaji ya kufanya ili basi

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unaweza kuwa sura hai tena.

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>> Hivyo factorial ya kuanza saa 4
mwanzo wa factorial.

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Ni 4 sawa na 1?

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Hakuna, hivyo ni kwenda kufanya kitu kimoja.

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Ni kwenda kwenda chini kingine tawi.

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Ni kwenda kupata kwamba mstari wa kanuni.

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OK, mimi nina kwenda na kurudi mara nne.

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Loo, factorial ya 3-- hivyo factorial ya
4 inategemea factorial ya 3 kumaliza.

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>> Na hivyo mahitaji kuwaita factorial ya 3.

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Na kwamba gonna kwenda kwa njia ya
mchakato huo tena.

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Ni kuanza kupitia, anapata hapa.

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Factorial ya 3 inategemea
juu ya factorial ya 1.

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Hivyo factorial ya 2 kuanza, anapata hapa.

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Ni inategemea factorial ya 1.

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Factorial ya 1 kuanza.

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>> SAWA.

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Hivyo sasa, sisi ni kupata
mahali fulani ya kuvutia, haki?

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Hivyo sasa, 1 ni sawa na 1.

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Na hivyo sisi kurudi 1.

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Katika hatua hii, sisi ni kurudi.

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Kazi inafanyika.

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Ni tabia is-- kuna
kitu kingine kwa ajili yake kufanya,

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na hivyo stack frame kwa
factorial ya 1 POP mbali.

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Ni kumaliza.

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Ni walirudi 1.

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Na sasa, factorial ya 2, ambayo
Ilikuwa sura mara moja chini yake

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katika stack, inakuwa sura hai.

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>> Na inaweza kuchukua
hasa ambapo kushoto mbali.

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Imekuwa ni kusubiri kwa factorial
cha 1 mpaka kumaliza kazi yake.

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Kwa sasa kumaliza.

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Na hivyo hapa sisi ni.

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>> Factorial ya 1 akarudi thamani ya 1.

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Hivyo factorial ya 2 can
kusema kurudi mara 2 kwa 1.

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Kazi yake kwa sasa unafanyika.

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Ni walirudi 2 kwa factorial
ya 3, ambayo ilikuwa kusubiri kwa ajili yake.

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Factorial ya 3 ni sasa sura ya juu,
sura hai katika stack.

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Na hivyo anasema, OK, vizuri, mimi nina kwenda
kurudi 3 mara 2, ambayo ni 6.

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Na mimi nina kwenda kutoa kwamba
thamani ya factorial nyuma

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ya 4, ambayo imekuwa kusubiri kwa ajili yangu.

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Nimemaliza.

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Factorial ya 3 POP mbali stack, na
factorial ya 4 sasa ni sura hai.

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>> 4 inasema, OK, mimi nina kwenda na kurudi mara 4
factorial ya 3, ambayo ilikuwa sita.

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Hiyo ilikuwa ni ya thamani kwamba
factorial ya 3 akarudi.

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Na hivyo mara 4 6 ni 24.

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Na mimi nina kwenda kupita
kuwa nyuma ya factorial

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5, ambayo imekuwa kusubiri kwa ajili yangu.

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Factorial ya 5 sasa ni sura hai.

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Ni kwenda na kurudi mara 5
factorial ya 4-- 5 mara 24, au 120--

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na kutoa thamani kwamba
nyuma kuu, ambayo ina

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wamekuwa wakisubiri kwa uvumilivu sana kwa
muda mrefu chini ya stack.

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>> Ni pale ulipoanzia.

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Ni alitoa wito huu.

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Muafaka kadhaa alichukua juu kwa juu.

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Sasa ni nyuma juu ya stack.

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Ni sura hai.

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Hivyo kuu got thamani 120
nyuma kutoka factorial ya 5.

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Imekuwa ni kusubiri kwa
magazeti nje thamani hiyo.

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Na kisha ni kosa.

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Hakuna mistari zaidi ya kificho katika kuu.

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Hivyo sura kuu ya POP mbali
stack, na sisi ni kosa.

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>> Na kwamba ni jinsi kujirudia kazi.

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Hiyo ni jinsi muafaka stack kazi.

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Wale wito kazi
yaliyotokea hapo awali

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ni tu juu ya pause, kusubiri
kwa ajili ya wito baadae

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kumaliza ili waweze kuwa hai
sura na kumaliza wanahitaji nini cha kufanya.

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>> Mimi nina Doug Lloyd.

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Hii ni CS50.

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