Programming MethodologyLecture25.docx
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Programming MethodologyLecture25.docx
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ProgrammingMethodologyLecture25
ProgrammingMethodology-Lecture25
Instructor(MehranSahami):
Sowelcomebacktoanotherfunfilled,excitingdayofcs106a.Acouplequickannouncementsbeforewestart.Firstannouncement,thereistwohandouts.Oneofthosehandouts,whichwe'llspendsometimetalkingabouttoday,isyourlastassignmentfortheclass,whichisassignmentNo.7.It'sworthnoting,wesortoftalkedaboutittheveryfirstdayofclasswhenwetalkedaboutlatedays.TheveryfirsthandoutsaysnolatedayscanbeusedonassignmentNo.7.Sothat抯importanttoremember.NolatedayscanbeusedforassignmentNo.7becauseit'sduethelastdayoftheclass.
Ifyou'relookingatthesyllabus,youmightsay,Ididn'tthinkwehadclassonFriday,thelastdayofclass.Thatwouldstillbecorrect.Wedon'tactuallyhaveclass,soyouonlyneedtodoelectronicsubmissionforturninginyourprogram,butit'sstilldueat3:
15onthatFriday.Wejustdon'tactuallyhavelectureonthatFriday.We'lltalkaboutthedetailsofthatassignmentaswegoalong.
TheotherhandoutthatyougotistheexampleofthecodethatyousaylasttimefortheFlyTunesmusicstore.Soyoushouldhaveallthatcode,whichshowsandexampleofabigdatastructure.Infact,thedatastructureforthatprogramisperhapsmorecomplicatedthanthedatastructureyou'regoingtoneedtouseforthefacepamphletassignment,No.7.
Soasyouknow,assignmentNo.6reviewtoday.Ihaveafeelingalotofpeoplemayhavebeentakinglatedaysonitbecauseitwas,forexample,thelastassignmenttoactuallybeabletouselatedayson.Sowe'lljustdoaquick,painfulastohowmuchtimeitactuallytookyou.Hopefullyitwasn'ttoopainful,butwe'llsee.
Justwondering,howmanypeoplearetakingalateday?
Wow.Soforthesixofyouwhoactuallyareturningintheassignmentontime,anyoneinthezerototwohourcategory?
Iwouldbefrightenedifyouwere.Idon'tthinkit'sactuallypossibletodointwohours.Maybe,ifyoujustsatthereandwroteallthecode.Twotofour?
Oh,Iactuallyhaveacouplefortwotofour.Wow.
Fourtosix?
Goodtosee.Ithinkallthe[inaudible]isjustgoingtobesmaller.Sixtoeight?
That'saprettyhealthycontingent.Eighttoten?
Alsogood-sizedcontingent.Tento12?
Coupleoffolks.12to14?
14to16?
16to18?
18plus?
Anyonein18plusandstillhasn'tturneditin,likeyou'rejustgoingforlatedays.Allright.That'sgood.
Sothat'sgoodtosee.It'sagoodtime.Worldisstillnormal,thoughthenormalcurvejusthappenstobealittlesmallerbecausethere'smorepeopletakinglatedays,butit'sagoodtime.Ifyouhaven'tdoneityet,twothings.Oneisthatthisshouldgiveyouanideaabouthowmuchtimeit'lltake,perhaps.Twoisyoudon'twanttopushit.Evenifyouhavelatedays,don'tpushitofftoolatebecauseyoureallywanttogiveyourselftimetodoassignmentNo.7.
Soanyquestionsaboutanythingwe'vedonesofarbeforewekindofdelveintotoday'sgreattopic?
Allright.SoIwanttospendthebeginningofclassactuallytalkingabitaboutyournextassignment.Soifyou'restillkindofinthemindsetofthinkingaboutnamesurfer,andyou'relike,oh,I'mjustsointhemindsetofassignmentNo.6,takethatlittlepartofyourheadthat'sgotassignmentNo.6.Popitoffthestack.That'smywholehead.Yeah,thatmightbepainful.Popitoffthestackforasecond,andwe'regoingtothinkaboutourfriend,thefacepamphlet.
Sojustaquickshowofhands,howmanypeoplearepartofasocialnetworkordosomesocialnetworkingonline.That'sgoodtosee.SoIwon'tneedtospendtoomuchtimetellingyouaboutwhatasocialnetworkis,butI'llspendalittlebitoftimeincaseyou'renotfamiliarwithsocialnetworks.
Basically,asocialnetworkisjustawayofkeepingtrackofsomesetofpeople,orprofilesofpeople,andrelationshipsamongpeople.Atthesimplestlevel,that'sallitis.Sowhatyoucanthinkaboutisyouhavesomeprofileforaperson.Insomesense,youcanthinkofthenotionofaprofileandapersoninterchangeablymostofthetime.Butasmostofyouknow,ifyou'veeverreadtheNewYorkerandseenthatcartoonthatnooneontheinternetknowsyou抮eadog.
Soyoudon'tnecessarilyhavetobeapersontohaveaprofile.Sowhenwethinkaboutasocialnetworkintheabstractsense,wealwaysjusttalkintermsofprofile.Butifwanttothinkaboutitconcretely,youcanjustthinkofaprofileasbeingsynonymouswithaperson,butitneednotbe,sowegenerallyrefertoaprofile.
Sowhataprofilehasassociatedwithit,ithassomeattributesorsomethingsthatwekeeptrackofforthatprofile.Forexample,ithasaname.Inthecaseofyourassignment,it'salsogoingtohavesomestatusthatwecareabout,keepingtrackoftheperson.Itmighthavesomeotherthings,likethereasonwhyitmightbecalledfacepamphletisbecausesayyouwanttokeeptrackofpeople'sfaces.Youwanttoactuallyseewhattheylooklike.
Soyoumightactuallyhavesomeimageinthere.ThenImentionedyouwanttokeeptrackofsomelistoffriends.Sothere'ssomenotionofalistoffriendsthatisalsoassociatedwithaprofile.Realsocialnetworksalsohaveotherthingsassociatedwiththem,andtheassignmenttalksaboutextensionsyoucando,butwe'renotgoingtogetintoextensionsrightnow.Butthesearethingswewanttothinkabout.
Foraperson'sprofile,there'saname.Oneofthethingsbasedonsomeoftheideaswetalkedaboutinthelastlecture,isyoucanthinkofnameasauniqueidentifier.Whatthatmeansisthatyouwillneverhavetwoprofilesinyoursocialnetworkthathavethesamename.Soonceyouhaveanameinyourprofile,inyoursocialnetwork,thatnameisyours.Thatprofilewillbeassociatedwiththatnameuntil,atsomepointwedecide,maybewewanttodeletetheprofiletogetridofit.Butthewholetimetheprofile'sactuallylive,itwillhavethatuniqueidentifier,whichisthenameofthatprofile.
Soifyouevertrytocreateanotherprofilewiththesamename,theapplicationwilltellyouthatyoucan't.I'llshowyousomeexamplesofthatinabit.Butthenameisauniqueidentifier,andthisthing'sjustsomestringthatwekeeptrackofthename.Soitcanbelikeyourrealnameorwhatevernameyouwanttohave,likeCodeDog.Thatcanbeyourprofilename.That'scool,too.
Statusisjustwhatyou'redoingrightnow.Youcanthinkofthisassomestringwhichiswhatyouhappentobeuptoatthetime.LikeMaronisteaching.Idon'tknow.Beniscontemplatinglife.It'sjustsomeparticularstringofthethingyouhappentobedoing.Youmightwanttochangethisafairbit.
Thisimagethingisjustanimage.Inourworld,thatmeansit'saGimage.Thatmeansit'ssomepicture.Originally,whenyoucreateaprofile,youmaynothaveastatus,andyoumaynothaveanimage.Youmaywanttoaddone.Youmaywanttochangeoneaslifegoeson.Weshouldbeabletoallowforthat.Thenyouhavealistoffriends.Whenyou'rebornintotheworld,yourlistoffriendsisempty.Overtime,youcangraduallybuildupfriends.
That'stheotherpartofthesocialnetworktoconsider,besidesthefactthatwehaveprofilesisthatwealsohavesomenotionoffriendship.Thewayyoucanthinkoffriendshipisbasicallysomeprofileorsomepersonjusthasalistoffriends.Soaneasywaytothinkofalistoffriendsisalistofnamesoffriendsbecausenamesareuniqueidentifiers.Soifwekeeptrackofalistofnames,wehavealistoftheuniqueidentifiersthatareourfriends.
That'saneasywaytobeabletolookthemup,forexample.Theideabehindfriendshipthat'skeytous?
thisisnotnecessarilytrueintherealworld,sadlyenough,butforourintentsandpurposes,asfarastheassignment'sconcerned,friendshipisreciprocal.Thatmeanstheifyourfriendshipisreciprocal.Notallthetime.That'sthewayitis.
WhatthereallymeansisifIhavetwopeople,likeIhaveBoboverhereandIhaveAliceoverhere,youcanthinkofthoseasprofiles.Iftheyarefriends,wedrawalinebetweentheirnamesinourlittlesocialnetwork.Thisisnotactuallyhowwekeeptrackofthemintheapplicationthatyou'llsee,butthisisoftenhowsocialnetworksaredrawn.
Weputinsortofacircleforeachprofileinthesocialnetwork.Here'sDonoverhere,andhere'sChelsea.Noticethere'stheABCDphenomenon.Alwaysagoodtime.Sowhenweputwhatwerefertoasalinkbetweentwopeople,thatmeansthey'refriends.Friendsarereciprocal.SoifBobisafriendofAlice,thatmeansthatAliceisafriendofBob.That'sjustthewaylifeisallthetimeinfacepamphlet.
It'sjustahappierplace.Everyone'slike,oh,I'llbeyourfriend.Okay.Thenyou'remyfriend,too.Sothat'sthewayyouwanttothinkaboutit.SoifBobeveraddsAliceasafriend,thatautomaticallymeansAlicebecomesBob'sfriend.There'sneveradirectionalityoffriendship.Bobclicks,oh,Alice,bemyfriend.She'slike,no.Talktothehand.Thathappensinreallifeallthetime,butnotherebecauseit'sjustahappierplacetobein.
Sothinkoffriendshipsasreciprocal.Again,wedon'tnecessarilyhavetohaveanythingexplicittomodelthislink.Allweneedtodoisthinkaboutjusthavingalistofnames.SoBobmighthaveAliceinhislistofnamesoffriendsthathe'skeepingtrackof.That'showIwouldkeeptrackofthelink.
Whatthatalsomeansisthatreciprocally,AliceshouldhaveBobinherlistoffriendsbecausethelinksarealwaysreciprocal.Whenweactuallydrawthisout,ifwewanttodrawthestylizedpicture,wecouldsayAliceisfriendswithChelseaandDon,andDonandChelseaareals
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