ReviewforFinalExamCS8:IntroductiontoComputerScience,Spring2019

Lecture#17

ZiadMatni,Ph.D.Dept.ofComputerScience,UCSB

Administrative•  Homework8duetoday!•  Lab6duetoday!

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FinalExamExtraReviewSessionFriday,June7th1:00–3:00PMPHELP2510

(thisisoptional)

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FinalsWeek•  Dr.Matniwillhaveofficehoursonfinalsweek

Monday 1:00pm–2:30pm

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•  Material:Everything!•  Homework,Labs,Lectures,Textbook•  Tuesday,6/11inthisclassroom•  Startsat4:00PM**SHARP**•  BringyourUCSBIDsandarrive10-15minutesearly•  Duration:3hourslong(butreallydesignedfor1.5–2hours)•  Closedbook:nocalculators,nophones,nocomputers•  Allowed:1sheet(double-sidedok)ofwrittennotes

–  Mustbenobiggerthan8.5”x11”–  Youhavetoturnitinwiththeexam

•  Youwillwriteyouranswersontheexamsheetitself.6/6/19 Matni,CS8,Sp19 5

ExampleofRecursiveFunctions:LinearSeries

•  MathematicalLinearSeriesExample:

S(n)=0,1,4,13,40,… forn=0to∞What’sthepattern?Linearseries: Sn+1=A.Sn+B whereA&BareconstantsIntheexampleabove: A=3andB=1Whatisourbase-case? Whatisourrecursion?

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Example:LinearSeries•  MathematicalLinearSeriesExample:

S(n)=0,1,4,13,40,… forn=0to∞Linearseries: Sn+1=3.Sn+1 and S0=0defseries(n):

ifn<=0: return0return(3*series(n-1)+1)

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recursion basecase

Example:RecursiveDrawing

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defdrawS(aTurtle,side):foriinrange(4):aTurtle.forward(side)aTurtle.right(90)defnestedBox(aTurtle,side):ifside>=1:drawS(aTurtle,side)nestedBox(aTurtle,side-5)

#Howcomethere’sno“base-case”??importturtlejim=turtle.Turtle()nestedBox(jim,100)

b/csidewilleventuallybe<1andtoosmalltodraw

MorePracticeQuestions!J

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ExerciseWhathappenswhenweusethemultiplyoperatoronalist,like:[1,2,3]*2?

① Iget[2,4,6]② Iget[1,2,3,1,2,3]③ Iget[[1,2,3],[1,2,3]]④ Igetanerrormessage

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ExerciseHowmanytimeswillthecharacter“x”printinthiscode?

①  7times②  6times③  5times④  4times⑤  Infinitetimes

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forminrange(3,9,2):print("x")n=mwhile(n<7):print("x")n+=7

Whatistheexactoutput?ucsb_classes=['CS8','CS16','CS24','ECON1','COMM88','MATH3A','CHEM6A']

l=[]

#Notethat:chr(65)=‘A’

forcinucsb_classes:

ifc[0]==chr(67):

l.append(c.lower()+"!")

print(l)

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ExerciseWriteaPythonfunction,AddG(s)thattakesastringsasaparameterandreturnsastringwith“g”aftereachcharacterintheoriginalstring.Forinstance:ifs="abcd"then,AddG(s)becomes"agbgcgdg”,orift="aog"then,AddG(t)becomes"agoggg”,

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Exercise•  Givenadictionary: D={1:0.1,2:0.2,3:0.3,4:0.4}•  Whatdoesthiscodedo?D2={}L=list(D.values())k=5forpinL: D2[k]=1+p k+=2print(D2)

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Itprints:{5:1.1,7:1.2,9:1.3,11:1.4}

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Example:ReversingaString•  RecursioninstringsExample:Reverseastring

Givenastring(e.g.“hello”),youwouldneedtoreturn“olleh”Whatdoesarecursivealgorithmlooklike?Whatismybase-case?

Hints:ifs=‘hello’,whatiss[1:]?defrevStr(s):iflen(s)==0:returnsreturnrevStr(s[1:])+s[0]

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