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>> [Music kucheza]

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DOUG LLOYD: zote haki.

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Aina ya mada ajabu, sawa?

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Idadi uchawi.

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Nini Doe yeye maana wakati yeye ni
kuzungumza juu ya idadi uchawi?

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Naam, baadhi ya mipango
kwamba tumekuwa yaliyoandikwa katika CS50

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hadi sasa wamekuwa na baadhi weird
idadi aina ya kutupwa ndani yao.

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Labda kwa sababu za hatufanyi
kabisa kuelewa hivi sasa.

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Kwa mfano, katika Mario tatizo, sisi
ulimalizika urefu wa piramidi katika 23.

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Sisi waziwazi alisema wewe
hawezi kwenda juu kuliko 23.

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>> Lakini ni nini 23 ina maana gani?

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Naam, kama wewe kusoma
spec kwa makini,

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aliyoiona kwamba
sababu sisi ulimalizika ni katika 23

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ni kwa sababu urefu kiwango cha
ya dirisha terminal ni 24.

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Na hivyo kama tuna
piramidi kuwa mrefu kuliko kwamba,

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inaweza kufanya jambo hili weird
ambapo ni anaendesha mbali screen.

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Na unajua, ni nini
Hiyo ina maana katika mazingira, haki?

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>> Ndio maana ya 23 mara moja dhahiri
kwa mtu ambaye anaangalia mpango wako

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na labda ina tofauti
ukubwa terminal dirisha?

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Pengine si.

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Inaonekana kama, Sawa.

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Naam, kwa nini ni tu chini ya 23?

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Kwa ujumla, ni aina
ya tabia mbaya kweli

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kuandika constants katika kanuni yako.

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Kwa kufanya hivyo, wakati wewe kweli kufanya
kuandika mara kwa mara katika kanuni yako,

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ni wakati mwingine hujulikana kama kutumia
idadi uchawi, ambayo ni kitu

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sisi ujumla wanataka kujaribu na kuepuka.

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>> Kwa mfano, hebu tuangalie
katika hafla hii rahisi hapa.

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Ni wazi hakuna data
aina katika C aitwaye kadi au staha.

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Hivyo tu kuzaa na mimi.

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Ni kidogo ya
pseudocode mchanganyiko katika hapa.

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Hii ni kazi kuitwa
kukabiliana kadi ambayo inaonekana

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inachukua staha kama parameter yake, na
mapenzi pato kwangu kadi moja.

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>> Na mimi nina kufanya kitu hapa ambapo mimi
na kitanzi kwamba anaendesha 0-52,

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na mimi kukabiliana kadi.

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Naam, sisi tumepewa uchawi
idadi katika hapa, hivi.

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Je, unaweza kuona nini idadi uchawi ni?

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Au muhimu zaidi, je,
kuona tatizo ni nini hapa?

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Hasa kama hii
ni kazi moja tu

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katika faili yake mwenyewe katika
folder kwamba ina

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rundo la tofauti
mafaili, ambayo kila mmoja

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anafanya jambo lingine karata.

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Labda ni shuffles yao, au inahusika mkono
kadi tano badala ya kadi moja.

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>> Je, unaweza kuona nini
tatizo inaweza kuwa hapa?

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Je, unaweza kuona idadi uchawi
Nimekuwa hudungwa katika kanuni?

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Ni 52, haki.

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>> Kama, shirikishi pengine kujua, sawa.

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Kama staha kiwango cha
kadi ina kadi 52.

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Lakini katika mpango wetu, ni tu
aina ya yaliyo karibu katika huko.

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Ni kama kwa ghafla kuna 52.

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>> Moja ya njia ya kutatua hili
Tatizo ni kufanya hivyo.

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Tuko wazi sana sasa
wito nje ukubwa staha kama 52.

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Ni anatoa ni Intuitive zaidi kidogo
maana wakati katika kwa kitanzi

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baadaye sisi basi sema, i
ni chini ya staha ukubwa.

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Ni tu inaonekana bora kuliko kusema 52.

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Sasa hii haina kweli kurekebisha tatizo.

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Haina kutoa baadhi ya ishara
maana kwa mara kwa mara.

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Lakini haina aina ya kweli
kuanzisha tatizo jingine

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kwamba wanaweza kuwa mara moja dhahiri.

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Hata kama kutofautiana hii
ni alitangaza globally--

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Je, unakumbuka kile
ina maana wakati sisi kutangaza

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kutofautiana kimataifa dhidi ya ndani ya nchi?

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Hata kama sisi kutangaza kutofautiana
kimataifa, kile kama kuna

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kazi nyingine katika
Suite yetu ya kazi

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kuwa mpango huo na kadi kudanganywa
kuwa inadvertently mabadiliko staha ukubwa,

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au ni ongezeko hilo kwa
1 au hupunguza na 1.

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Ambayo inaweza Spell shida, sawa?

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Hasa kama sisi ni kushughulika na seti
kadi ambapo shuffling staha kamili

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inahitajika.

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Kama staha ukubwa hupungua
kwa 1, kwa mfano, 51,

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sisi siyo kweli shuffling
kadi zote uwezekano.

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Sisi ni kuacha moja ya yao nje.

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Na thamani kwamba pengine zinaweza kuwa
alikadiria au kunyonywa na muigizaji mbaya.

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>> C hutoa kile kinachoitwa
preprocessor agizo, ambayo

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Pia inaitwa uchumi mkuu kwa
kujenga constants ya mfano.

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Na kwa kweli, wameweza tayari
kuonekana preprocessor agizo,

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hata kama wewe si habari hiyo
aitwaye kwamba kwa pamoja na #.

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Ni mfano mwingine wa uchumi mkuu
au preprocessor agizo.

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>> Njia ya kujenga constants ya mfano,
au kutoa jina kwa mara kwa mara

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hivyo kwamba ina zaidi
maana, ni kama ifuatavyo.

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#define, jina, uingizwaji.

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Kweli ni muhimu kando
hapa kweli haraka.

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Je, si kuweka semicolon katika
Mwishoni mwa # amefafanua yako.

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Hivyo ni # define, jina, uingizwaji.

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>> Wakati mpango wako ni ulioandaliwa,
nini hasa kinatokea

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ni mkusanyaji kama kwenda
kupitia kanuni yako

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na badala kila mfano wa
neno "jina" na chochote

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kuweka kama badala.

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Kama mfano, ikiwa ni pamoja na # ni aina
ya sawa na kuiga na pasting,

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kisha # define ni aina ya
sawa na kupata na kuchukua nafasi,

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kama wameweza milele kutumika kipengele kwamba katika
neno usindikaji mpango, kwa mfano.

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>> Hivyo kwa mfano, kama mimi
#define pi kama 3.14159265,

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kama wewe ni bora hesabu
kutega na ghafla

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ona 3.14159265 kuruka
kuzunguka katika kanuni yako,

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pengine kujua ni kuzungumza juu pi.

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Lakini labda tunaweza kuwapa
kidogo zaidi ya mfano maana.

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Na tunaweza badala kusema # define
pi kama kuwa Mouthful ya namba

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kwamba mimi si kwenda kuweka
kusoma tena na tena.

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>> Na nini kitatokea basi katika
kukusanya wakati ni wakati mpango huo ni

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ulioandaliwa, Jambo la kwanza kwamba
kitatokea ni itakuwa kupitia

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na itakuwa nafasi kila wakati
anaona mji mkuu P, mji mkuu mimi,

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kutakuwa na halisi badala yake pamoja na
3.14 na kadhalika, ili uweze

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huna aina yake kila
muda wakati mpango wako bado

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ina utendaji kwamba
kutarajia, kwa sababu wewe ni kufanya kazi

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na manipulating, kuzidisha,
kugawa, chochote ni na pi.

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>> Wewe si mdogo kwa hii
badala ya namba tu.

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Kwa mfano, mimi naweza # define
Bila shaka kama kamba CS50.

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Katika kesi hiyo, wakati
mpango ni ulioandaliwa,

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#define watapitia
kanuni, kuchukua nafasi ya kila wakati

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anaona "bila shaka" kwa kamba CS50.

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>> Utagundua hapa
pia kwamba mimi mara nyingi

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#define wangu wote inavyoelezwa ishara
constants, hivyo kusema,

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ni siku zote katika mechi zote.

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Ni mkataba.

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Ni si required.

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Sababu kwa ujumla watu watatumia
miji mikuu yote wakati wao ni #defining

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ni tu kufanya ni kweli wazi kuwa
kipengele fulani ya kanuni yangu

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ni mara kwa mara defined.

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Kama ilikuwa ndogo, inawezekana kwamba
inaweza kuwa na kuchanganyikiwa na kutofautiana.

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Na kwamba pengine
si jambo zuri la kufanya.

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>> Hivyo hii hasa
ufumbuzi ni bora zaidi

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kuliko aidha ya zile za nyuma.

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Kama mimi #define kwanza staha ukubwa 52, kisha
sasa matumizi yangu ya 52, au staha ukubwa hapa,

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ni mengi zaidi Intuitive na mengi salama.

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Huwezi kuendesha mara kwa mara.

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Huwezi kusema 52 pamoja pamoja.

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Hiyo si kwenda kubadilisha kwa 53.

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Huwezi kubadili 52 na kitu.

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>> Unaweza kubadilisha kutofautiana
ambao thamani ni 52,

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ambayo ilikuwa kurekebisha kwanza tulikuwa na kabla.

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Na unaweza kuongeza
kwamba kutofautiana kwa 53.

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Lakini huwezi kusema 52 pamoja pamoja na
na kwamba ghafla kugeuka 52 katika 53.

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52 ni siku zote 52.

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Na hivyo huwezi kubadili inadvertently
staha ukubwa hapa kwa kufanyia hayo,

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>> Mwingine upande mzuri
athari za ingawa hii ni

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ambazo ni wewe na ufahamu kwamba si
nchi zote duniani

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kutumia karata ya ukubwa 52?

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Kwa mfano, ni kweli ya kawaida katika
Ujerumani kutumia ukubwa staha ya 32,

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ambako strip nje baadhi
ya chini thamani kadi.

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Na katika kesi hii, mimi
alitaka bandari Suite yangu

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ya kazi ambayo kukabiliana na
kadi kudanganywa kwa Ujerumani.

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Mimi naweza kwa mara ya kwanza sisi
ilionyesha, una kwenda na badala

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00:06:59,440 --> 00:07:03,570
matukio yote ya 52 katika kanuni wangu na 32.

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00:07:03,570 --> 00:07:07,940
>> Lakini hapa, kama mimi #define staha ukubwa
kama 32 katika sana juu ya kanuni yangu,

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kama mimi haja ya mabadiliko hayo, siwezi
tu kwenda na mabadiliko hayo jambo moja.

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Recompile kificho wangu, na yote ya
ghafla ni kueneza kupitia.

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Kwa kweli, tunaweza kubadili staha
ukubwa kwa thamani yoyote tunataka.

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>> Naweza maslahi yenu katika
mchezo wa staha ukubwa Pickup?

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00:07:22,500 --> 00:07:23,430
>> Mimi nina Doug Lloyd.

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00:07:23,430 --> 00:07:25,840
Na hii ni CS50.

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