Listoflectures
TDDA69DataandProgramStructure
ImperativeProgramming
andDataStructures
CyrilleBerger
1IntroductionandFunctionalProgramming
2ImperativeProgrammingandDataStructures
3Parsing
4Evaluation
5ObjectOrientedProgramming
6Macrosand
7VirtualMachinesandBytecode
8GarbageCollectionandNativeCode
9DistributedComputing
10DeclarativeProgramming
11Logic
12Summary
2/59
Lecturecontent
ImperativeProgramming
Statements
ConditionalStatement
IterativeStatements
ImperativeProgramming
Advantages/
Datastructures
Arrayand
Arrayvslistvs
Tree
TreeWalking
TreeRecursion
Dictionnary
3/59
Whatisimperativeprogramming?
Foundationsofimperativeprogramming
Expresshowcomputationare
executed
MosthardwarefollowtheVonNeumannarchitecture,whichisimperative
CentralProcessingUnit
Describescomputationintermofstatements
thatchangetheinternalstate
Verysimilartorecipes
Inputdevice
Examples:C/C++,Pascal,
Java,Python,JavaScript...
ControlUnit
Arithmetic/LogicUnit
Outputdevice
MemoryUnit
Manyoftheearlyimperativeprogramminglanguages(Fortran,C...)are
abstractionsofassemblylanguage
ExampleofnonVonNeumann:FPGA(reconfigurablecomputer
architecture)
5
6
Statements
Statements
Astatementisexecutedbythe
interpretertoperformanaction
Statement
<header>:
<statement>
<statement>
...
<statement>
<optionalseparatingheader>:
<statement>
<statement>
...
<statement>
...
Suite
Clause
8
Expressionstatements
Assignmentexpression
Sameexpressionsasinfunctional
programming
2
plus
'hello'
max
(
2
,
Compoundexpressions
3
Assignmentexpression
a=2;a:=2;a<-2;(seta2)...
Global
)
max(min(pow(3,5),-4),min(1,-2)*2)+6
9
10
ConditionalStatement
ConditionalStatement
Astatementthatperformdifferent
computationsdependingona
booleanexpression
12
if/else
InPython:
defabs_val(x):
if(x<0):
return-x
elif(x==0):
return0
else
returnx
ImperativeconditionvsFunctionalcondition
Imperative:
functionabs_val(x)
{
varresult;
if(x<0)
{
result=-x;
}elseif(x===
0)
{
result=0;
}else{
result=x;
}
returnresult;
}
InECMAScript/JavaScript:
functionabs_val(x)
{
if(x<0)
{
return-x;
}elseif(x===0)
{
return0;
}else{
returnx;
}
}
Howmanystatementsintheabs_valfunction,
inPython?InECMAScript?
www.govote.at841887
start
Functional:
functionabs_val(x)
{
returncond(x<0,
-x,
cond(x===
0,
0,
x);
}
13
Whatdoesthisprogramoutput?
x=2
y=4
ifx==y2:
print("a")
else:
print("b")
ifx:
print("c")
else:
print("d")
ifx-2:
print("e")
else:
print("f")
14
Booleanexpressions
InPython:
Falsevalues:False,0,'',None,0.0,[],{},()
Truevalues:anythingelse(True,1,2,'hello'...)
www.govote.at575853
start
15
16
switch
Conditionalswitchbasedonthevalueofan
switch(a)
{
case0:
dosomething;
break;
case'hello'
dosomethingelse;
break;
caseTrue:
dosomeother
thing;
break;
}
Thisisnotjustsyntaxic
IterativeStatements
itgivesperformanceadvantage
17
Whileloop
Forloop
Allowstatementstobeexecuted
repeatedlyaslongasa
conditionhold
Convenientstatementforloopingon
ranges
InJavaScript/ECMAScript:
vartotal=0;
for(vari=0;i<3;++i)
{
total=total+i;
}
InPython:
total=0
foriinrange(0,3):
total=total+i
i,total=0
whilei<3:
i=i+1
total=total+i
19
20
Breakstatements
Exitthecurrentloop
i,total=0
whileTrue:
i=i+1
total=total+i
ifi<3:
break;
Advantages/Incovenients
21
Inconvenients
ImperativeProgramming'sstrength
Naturalwayofexpressingprograms:
Closetothe
Programsarewrittenasalistof
Moreefficientthanfunctional
Popular
Statesareuseful
StatesinducesideUnexpectedbehavior
Datarace
Simulations
Howdoyouimplementafunctional
randomnumbers?
23
24
Datastructures
ArrayandList
Array
Whyshouldarrayindexstartsat0?
Collectionofelements,identified
byanindex
Indexusuallystartsat0
untillength-1
Arraysallowrandom
Historically,inC,arraysareimplementedas
pointers
Dijkstrasuggeststhatthenaturalnotationto
denoteasubsequenceofnaturalnumbers
shouldhavethefollowingproperties:
1Thesubsequenceincludesthesmallestnaturalnumber,0
2Thesubsequenceisempty
Forthenumbersatob,wecanrepresentit
vararray=[1,4,8]
console.log(array[0].array[1],array[2]);
1a<i<b
2a≤i<b
3a<i≤b
4a≤i≤b
27
28
(Linked-)List
ListOperations
A(linked-)listisasequenceof
valueswhereeachentry
containsapointertothenext
1
element
4
8
Operationsonlist
Constructorforcreatinganemptylistnew_list
Testifalistisemptyis_empty
Prependanelementtothelistprepend
Appendanelementtothelistappend
Returnthefirstelementhead
Returnalltheelementsexceptthefirsttail
ø
29
ExampleofListImplementation(1/3)
30
ExampleofListImplementation(2/3)
Eachelementisatwoelements
Eachelementisatwoelementsarray
varlist=[1,[4,[8,null]]]
Thefirstelementisthe
ThesecondisthenextelementoranullExample:varlist=[1,[4,[8,null]]
Prependanelement:
deflist_prepend(arr,val):
if(list_is_empty(arr)):
arr.append(val)
arr.append(None)
else:
arr[1]=[arr[0],arr[1]]
arr[0]=val
returnarr
Constructor:
def
list_new():
return[]
Emptytest:
Appendanelement:
deflist_append(arr,val):
if(list_is_empty(arr)):
arr.append(val)
arr.append(None)
else:
ptr=arr
while(ptr[1]!=None):
ptr=ptr[1]
ptr[1]=[val,None]
returnarr
def
list_is_empty(arr):
returnlen(arr)==0
31
Suggestasolutionto
improvetheappendfunction
www.govote.at9943
32
Double-endedqueue
ExampleofListImplementation(3/3)
Adouble-endedqueue(deque):
arrayforwhichelementscanbe
addedatthefrontoratthe
back
Implemented:
Eachelementisatwoelements
varlist=[1,[4,[8,null]]
Returnthefirstelement:
def
list_head(arr):
returnarr[0]
Returnalltheelementsexcept
circularbuffer
centeredinanarray
storedinmultiplearrays
thefirst:
def
list_tail(arr):
returnarr[1]
33
34
Performance(1/3)
Insertionattheback
Arrayvslistvsdeque
Insertionatthefront
Source:http://baptiste-wicht.com/posts/2012/12/cpp-benchmark-vector-list-
36
Performance(2/3)
Performance(3/3)
Randominsertion
Linearsearch
Random
Sort
Source:http://baptiste-wicht.com/posts/2012/12/cpp-benchmark-vector-list-
Source:http://baptiste-wicht.com/posts/2012/12/cpp-benchmark-vector-list-
37
Arrayvslist
38
Tuple
Arrays:random-access,efficient
unlessyouneedtoresize
Lists:accessthroughiteration,
o(1)forinsertion
orderedlistofelements
InPython:
Notmutablelist
Convenientforfunctionreturn:
defmake_tuple(a,b,c):
return(a,b,c)
(a,b,c)=make_tuple(1,2,3)
39
40
Iterating
Usingthearrayindex:
Usingthearrayindex:
Usingforeach:
Usingforeach:
functionprint_arr(arr)
{
for(vari=0;i<arr.length;+
+i)
{
console.log(arr[i])
}
}
functionprint_arr(arr)
{
for(varvalofarr)
{
console.log(val)
}
}
Range
Arangeisasequenceof
range(startingvalue,
endingvalue)
defprint_arr(arr):
i=0
while(i<size(arr)):
print(arr[i])
range(-2,2)->[-2,-1,0,1]
Usefulinforloop
defprint_arr(arr):
for(valinarr):
print(val)
foridxinrange(0,arr.length):
print(arr[idx])
Orinfunctionalprogramming:
(take25(squares-of(integers)))
41
42
Tree
Tree
Atreeiseitherasinglevalue
calledaleaforasequence
oftrees
1
2
4
ø
8
ø
44
ExampleofTreeImplementation
Usinganarray
Thefirstelementisthevalue
Thesecondisalistofchildren
Example:
[1,[[2,[]],[4,[[8,[]]]]]]
defcreate_tree(val,*children):
return[val,list(children)]
tree=create_tree(1,create_tree(2),
create_tree(4,create_tree(8)))
TreeWalking
45
Visitor
Listener
Atreelistenerisatypeoftreewalking
whereafunctioniscalledwhen
enteringanodeandwhenexitingit
Atreevisitorisatypeoftreewalkingthenodesintreeare
visitedrecursively
deftree_visitor(tree):
if(len(tree[1])==0):
return1
val=1
forcintree[1]:
val=max(val,tree_visitor(c))
returnval+1
deftree_listener(tree,entering,exiting):
entering(tree)
forcintree[1]:
tree_listener(c,entering,exiting)
exiting(tree)
tree_visitor([1,[[2,[]],[4,[[8,[]]]]]])>>
www.govote.at289943
start
HowwellwouldthatworkinPythonforinfinitelydeep
trees?
defprint_node(tree):
print(tree[0])
tree_listener(tree,print_node,print_node)
Why?www.govote.at3036
start
47
48
TreeRecursion
Tree-shapedprocessesarisewhenever
executingthebodyofarecursivefunction
makesmore
TreeRecursion
n:0,1,2,3,4,5,6,7,8,...,35
fib(n):0,1,1,2,3,5,8,13,21,...,9227465
deffib(n):
ifn==0:
return0
elifn==1:
return1
else:
returnfib(n-2)+
50
ATree-RecursiveProcess
RepetitionnTree-RecursiveComputation
Thecomputationalprocessoffib
evolvesintoatreestructure
Thisprocessishighlyrepetitive;fibiscalledonthesame
argumentmultipletimes.
fib(5)
fib(5)
fib(4)
fib(4)
fib(3)
fib(3)
fib(2)
fib(1)
fib(2)
fib(1)
fib(1)
fib(2)
fib(0) fib(1)
fib(3)
fib(3)
fib(1)
fib(0)
fib(2)
fib(1)
fib(0)
fib(2)
fib(1)
fib(1)
fib(2)
fib(0) fib(1)
fib(1)
fib(0)
fib(0)
Howwouldyouimprove?
www.govote.at5346
start
51
52
Memoization
Memoization:storeresultsofexpensivefunction
calls
__fib_cache={0:0,1:1}
deffib_cached(n):
ifnin__fib_cache:
return__fib_cache[n]
else:
__fib_cache[n]=fib_cached(n-2)
+
fib_cached(n-1)
return__fib_cache[n]
Dictionnary
Timing:
fib(9000)->>aweek
fib_cached(9000)->8.77ms(arrayversion
fib_fast_doubling(9000)->6.1ms
53
Dictionnary
DictionnaryOperations
Adictionnaryisanassociativearray,where
eachelementisassociatedtoanindex
Typeofindex,anythingthatcanbeordered(with
<)orcomparedandandevenbetterifahashcan
becomputed
Creationofadictionnary:
defdict_create():
return[]
Setavalue:
defdict_set(h,nk,nv):
foriinrange(0,len(h)):
(k,v)=h[i]
if(k==nk):
h[i]=(nk,nv)
return
h.append((nk,nv))
Integer,notnecesseralycontinuous
Strings
Example:
Getavalue:
varmap={1:0,'hello':'world'}
console.log(map[1],map['hello'])
Inmanydynamicobjectoriented
programminglanguages,Objectsare
Dictionnaries:Python,JavaScript/
ECMAScript...
defdict_get(h,nk):
foriinrange(0,len(h)):
(k,v)=h[i]
if(k==nk):
returnv
returnNone
end{pythoncode}
55
56
Hashmap
HashmapOperations
Inahashmapahashofthekeyiscomputed,
usingthathashthevaluesarestoredindifferent
bucket
Ahashfunctionisafunctionthatmaparbitrary
datatofixsize
Examples:
Createahashmap:
defhashmap_create(hash_function,
buckets):
hash=[hash_function,buckets,[]]
foriinrange(0,buckets):
hash[2].append(dict_create())
returnhash
Setavalue:
defhashmap_set(hashmap,key,value):
key_hash=hashmap[0](key,hashmap[1])
dict_set(hashmap[2][key_hash],key,value)
defhash_integer(k,m):
returnk%m
defhash_string(k,m):
h=0
forcink:
h=h+ord(c)
returnh%m
Getavalue:
57
Summary
Imperativeprogramming
Data
59/59
defhashmap_get(hashmap,key):
key_hash=hashmap[0](key,hashmap[1])
returndict_get(hashmap[2][key_hash],
key)
58