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Doug LLOYD: Jekk inti stajt tidher
l-video fuq recursion,

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il-proċess kollu jista 'jkollhom
deher ftit maġika.

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Kif taħdem?

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Kif il-funzjonijiet jafu li
bżonn li tistenna u stenna għall-valur ieħor

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li jirritornaw minn funzjoni differenti
sejħa sabiex tikseb ir-riżultat li rridu?

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>> Ukoll, ir-raġuni dan jaħdem huwa għaliex
ta 'xi ħaġa magħrufa bħala l-munzell sejħa.

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Meta inti sejħa funzjoni, il-
sistema twarrab ispazju fil-memorja

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għal dik il-funzjoni li jagħmlu xogħol tagħha.

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U aħna sejħa dawn biċċiet ta 'memorja li
qed jiġu mwarrba għal kull funzjoni

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sejħa qafas munzell jew qafas funzjoni.

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U kif inti tista 'tistenna,
dawn il-frejms munzell

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jgħixu fuq il-parti munzell ta 'memorja.

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>> Qafas munzell aktar minn funzjoni waħda
jista 'jeżisti fil-memorja fi żmien partikolari.

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Jekk ewlenija jitlob mossa funzjoni,
u jimxu jitlob direzzjoni,

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it-tliet funzjonijiet jkollhom frames miftuħa.

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Iżda dawn mhux kollha għandhom frames attivi.

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Dawn l-oqsfa huma rranġati munzell.

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U l-qafas tal-
aktar reċentement imsejjaħ

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funzjoni huwa dejjem fuq quċċata tal-munzell.

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U li huwa dejjem l-qafas attiva.

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Hemm biss verament qatt wieħed
funzjoni li l-attiv fi żmien.

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Hu l-waħda fuq quċċata tal-munzell.

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>> Meta funzjoni jitlob ieħor
funzjoni, huwa tip ta 'preses nieqaf.

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Huwa tip ta 'huwa fuq istiva, stennija.

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U l-qafas munzell ieħor hu imbuttata
fuq il-munzell fuq quċċata ta 'dan.

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U li ssir l-qafas attiva.

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U l-qafas immedjatament
hawn taħt jeħtieġ li tistenna

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sakemm għal darb'oħra huwa l-qafas attiva
qabel ma tkun tista jkompli b'ħidmietu.

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Meta funzjoni hija
kompluta u dan isir,

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frejm tagħha huwa popped off-munzell.

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Dik hija l-terminoloġija.

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U l-qafas immedjatament
taħtu, kif I biss qal,

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isir il-qafas attiva ġdida.

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>> U jekk jitlob funzjoni oħra,
li għaddej biex nieqaf mill-ġdid.

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Qafas munzell dik il-funzjoni ġdida se
jiġu mbuttati fuq il-quċċata tal-munzell.

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Hija ser jagħmlu xogħol tagħha.

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Jista pop lura off.

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U l-funzjoni oħra
taħtha tista 'tkompli mill-ġdid.

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>> Mela ejja jmorru permezz ta 'dan mill-ġdid, tfittex
fuq l-idea tal-funzjoni fattorjali

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li aħna definit fil-
recursion video biex tara

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eżattament kif l-magic wara dan
proċess rikursivi qed iseħħ.

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Allura dan huwa fajl sħiħ tagħna, id-dritt?

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Aħna definiti żewġ
functions-- prinċipali u fatt.

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U kif aħna tista 'tistenna,
kwalunkwe programm C va

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li jibda fl-ewwel linja ta 'prinċipali.

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>> Allura aħna joħolqu qafas ġdid munzell għall prinċipali.

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U li għaddej biex tibda taħdem.

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Sejħiet ewlenin printf.

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U printf se
jistampa fattorjali 5.

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Ukoll, hija ma kinitx taf
liema fattorjali ta '5 huwa,

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u għalhekk din is-sejħa huwa diġà
jiddependi fuq sejħa funzjoni oħra.

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Allura prinċipali se nieqaf hemm dritt.

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Jien gonna leave tagħha
vleġġa hemm dritt, kulur

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l-istess kulur bħat-
munzell qafas fuq il-lemin,

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biex jindikaw li ewlieni se jiffriża
hawn filwaqt fattorjali tal-5 tissejjaħ.

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>> Allura fattorjali ta '5 tissejjaħ.

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U li għaddej biex tibda fil-ħafna
bidu tal-funzjoni fattorjali.

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Hija tqajjem il-mistoqsija am I ugwali għal 1?

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Huwa 5 ugwali għal 1?

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Well, no.

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Allura li għaddej biex jinżlu għal
il-parti inkella, ritorn n ħinijiet

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fattorjali ta 'n minus 1.

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Well, OK.

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>> Allura issa, fattorjali ta '5 huwa
jiddependi fuq sejħa oħra

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li fattorjali, li jgħaddi
f'4 bħala l-parametru.

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U għalhekk l-fattorjali ta
5 qafas, dak il-qafas aħmar,

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se friża hemm dritt
f'dak linja stajt indikat

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u stenna għal fattorjali ta '4 biex jintemm
dak li jeħtieġ li jsir dan li allura

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tista 'ssir l-qafas attiva mill-ġdid.

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>> Allura fattorjali ta '4 jibda fil
il-bidu ta 'fattorjali.

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Huwa ta '4 ugwali għal 1?

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Le, hekk li għaddej biex jagħmlu l-istess ħaġa.

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Li għaddej biex jinżlu l-fergħa ieħor.

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Li għaddej biex tikseb sa dik il-linja tal-kodiċi.

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OK, jien ser jirritorna erba 'darbiet.

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Oh, fattorjali ta 3-- hekk fattorjali ta
4 tiddependi fuq fattorjali tat-3 irfinar.

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>> U għalhekk għandha bżonn iddur fattorjali ta '3.

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U li gonna jgħaddu
l-istess proċess mill-ġdid.

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Huwa jibda permezz, gets hawn.

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Fattorjali ta 3 jiddependi
fuq fattorjali ta '1.

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Allura fattorjali ta '2 tibda, gets hawn.

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Hija tiddependi fuq fattorjali ta 1.

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Fattorjali ta '1 jibda.

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>> KOLLOX SEW.

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Allura issa, aħna qed jkollna
x'imkien interessanti, right?

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Allura issa, 1 huwa ugwali għal 1.

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U hekk nerġgħu lura 1.

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Wara dan, aħna qed jirritornaw.

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Isir il-funzjoni.

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Huwa imġieba is-- hemm
xejn biex din tagħmel,

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u għalhekk il-qafas munzell għall
fattorjali ta '1 pops off.

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Huwa lest.

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Hija lura 1.

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U issa, fattorjali ta '2, li
kien il-qafas immedjatament taħt it

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fil-ċmieni, isir il-qafas attiva.

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>> U jista 'pick up
eżattament fejn jitħalla 'off.

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Huwa ilhom jistennew għal fattorjali
minn 1 sa jintemm ix-xogħol tagħha.

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Huwa issa lest.

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U hekk aħna qegħdin hawn.

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>> Fattorjali ta 1 ritornati valur ta '1.

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Allura fattorjali ta 2 jista
jiġifieri ritorn 2 darbiet 1.

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Il-ħidma tiegħu issa qed isir.

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Huwa lura 2 sa fattorjali
ta '3, li kienet qed tistenna dan.

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Fattorjali ta '3 issa huwa l-qafas ta' fuq,
l-qafas attiva fil-ċmieni.

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U għalhekk jgħid, OK, ukoll, jien ser
li jirritornaw 3 darbiet 2, li huwa 6.

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U jien ser jagħti dak
valur lura għall fattorjali

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ta '4, li baqgħet tistenna lili.

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Jien jsir.

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Fattorjali ta '3 pops off-munzell, u
fattorjali ta '4 issa huwa l-qafas attiva.

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>> 4 jgħid, OK, jien ser jirritorna 4 darbiet
l fattorjali ta '3, li kien sitta.

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Dan kien ta 'valur li
fattorjali ta '3 lura.

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U hekk 4 darbiet 6 huwa 24.

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U jien ser jgħaddu
li lura għall fattorjali

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ta '5, li baqgħet tistenna lili.

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Fattorjali ta '5 issa hija l-qafas attiva.

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Huwa ser jirritorna 5 darbiet
fattorjali ta 4-- 5 darbiet 24, jew 120--

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u tagħti lil dak il-valur
lura għall prinċipali, li għandha

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ilhom jistennew patiently ħafna għal
żmien twil fil-qiegħ tal-munzell.

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>> Huwa fejn bdiet.

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Hija magħmula din is-sejħa.

123
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Diversi frames ħadet fil-quċċata.

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Issa huwa lura fuq nett tal-munzell.

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Hu l-qafas attiva.

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Allura prinċipali ltqajna l-valur 120
lura mill fattorjali ta '5.

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Huwa kien stennija biex
jistampa dak il-valur.

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U allura dan isir.

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M'hemm l-ebda aktar linji ta 'kodiċi fil prinċipali.

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Allura frame prinċipali ta pops off
il-munzell, u aħna qed isir.

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>> U li kif recursion xogħlijiet.

132
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Thats kif frames munzell jaħdmu.

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Dawk is-sejħiet funzjoni
li ġara qabel

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huma biss fuq pause, stennija
għas-sejħiet sussegwenti

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biex jintemm sabiex ikunu jistgħu jsiru l-attivi
frejm u finitura dak li għandhom bżonn biex jagħmlu.

136
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>> Jien Doug Lloyd.

137
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Dan huwa CS50.

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