CS1102 Tut 1 ADTs

1
CS1102 Tut 1 ADTs

• Max Tan
• tanhuiyi_at_comp.nus.edu.sg
• S15-03-07 Tel[phone]

2
Test yourself

• Question In parameter passing in Java methods
• (1) Java pass by value
• (2) Java pass by reference
• (3) Java pass by value for primitives and
  reference for non-primitives

3
Bonus Question

• public class Tester
• static Person b new Person()
• public static void main(Stringargs)
• Person a new Person()
• a.setName("Fred")
• b.setName("Peter")
• changeName_1(a)
• System.out.println(a.getName() " "
  b.getName())
• changeName_2(a)
• System.out.println(a.getName() " "
  b.getName())
• public static void changeName_1(Person a)
• b new Person()
• b.setName("David")
• a b

class Person private String name
public void setName(String name)
this.name name
public String getName()
return this.name
4
Last week..

• What is the output ?
• To understand this problem, we must understand
  how Java handle variable names
• When we declare a non-primitive variable, the
  variable contains the address to the object and
  NOT the object itself
• Recall Primitive variables are int, double,
  float etc..

5
Last week..

• Person a new Person(Michael)
• //When the new keyword is used, a new object is
  created. Variable a is updated to store the
  address of this object
• Person temp a
• //In this step, the address of object pointed to
  by a is copied into temp. The object is not
  copied

6
Bonus Question

• public class Tester
• static Person b new Person()
• public static void main(Stringargs)
• Person a new Person()
• a.setName("Fred")
• b.setName("Peter")
• changeName_1(a)
• System.out.println(a.getName() " "
  b.getName())
• changeName_2(a)
• System.out.println(a.getName() " "
  b.getName())
• public static void changeName_1(Person a)
• b new Person()
• b.setName("David")
• a b

class Person private String name
public void setName(String name)
this.name name
public String getName()
return this.name
7
Question 1
8
Question 1
9
Question 1

• a.setName(Fred)
• b.setName(Peter)
• changeName_1(a)
• //a.name Fred, b.name David
• changeName_2(a)
• public static void changeName_2(Person a)
• a.setName("John")
• //output John David

10
Question 1
11
How this relates to LinkedList

• class Listnode String value ListNode
  next public Listnode(String s) value
  s

Next just stores the address of the next
listnode.
12
How this relates to LinkedList

• Listnode n1 new Listnode(a)
• Listnode n2 new Listnode(b)
• Listnode n3 new Listnode(c)
• n1.next n2
• n1.next.next n3

What is n1.next ?
13
Another example
head
temp

• head.next.next.prev.next.next.prev temp
• This is an assignment operation!
• You are setting the previous pointer of some node
  to temp!

14
Another example
head
temp

• head.next.next.prev.next.next.prev temp
• How do you determine which node?
• Step by step

15
Another example
head
temp

• head.next.next.prev.next.next.prev temp
• head is node 3

16
Another example
head
temp

• head.next.next.prev.next.next.prev temp
• Head.next is node 12

17
Another example
head
temp

• head.next.next.prev.next.next.prev temp
• head.next.next is node 32

18
Another example
head
temp

• head.next.next.prev.next.next.prev temp
• head.next.next.prev is node 12

19
Another example
head
temp

• head.next.next.prev.next.next.prev temp
• head.next.next.prev.next.next is node 35
• So, essentially the statement is saying node
  35.prev temp

20
Group assignment

• Question 1 Group 4
• Question 2 Group 1
• Question 3 Group 2
• Question 4 Group 3
• Question 5 Group 4
• Question 6 Group 1

21
q1

• Consider an ADT List of integers. Write the
  method
• int addList(List aList) throws ListOutOfBoundsExce
  ption
• that computes the sum of the integers in the list
  aList. The operations on list are

• createList()
• isEmpty ()
• size ()
• add (newPosition, newItem)
• remove (index)
• removeAll ()
• get (index)

22
q1 solution

• int addList(List aList) throws ListOutOfBoundsExce
  ption
• // ----------------------------------------------
  ------------
• // Computes the sum of the integers in the list
  aList.
• // Precondition aList is a list of integers.
• // Postcondition The sum of the integers in
  aList is returned.
• // ----------------------------------------------
  ------------
• int sum 0, nextItem
• for(int i 1 i lt aList.size() i)
  
• nextItem aList.get(i)
• sum nextItem
• // end for
• return sum
• // end AddList

23
q2

• Implement the method swap (aList, i, j) that
  interchanges the items currently in positions i
  and j of a list. Define the method in terms of
  the operations of the ADT List so that it is
  independent of any particular implementation of
  the list. Throw an exception ListIndexOutOfBoundsE
  xception if i and j is out of range.

24
q2

• What are the useful operations you can use in the
  ADT list ?
• get()
• remove()
• add()
• set()

25
q2 solution

• void swap(List aList, int i, int j) throws
  ListOutOfBoundsException
• // ----------------------------------------------
  ---------
• // Swaps the ith and the jth items in the list
  aList.
• // Precondition aList is a list of type
  Object.
• // Postconditions The ith and jth items are
  swapped in aList
• // ----------------------------------------------
  ---------
• Object first, second
• first aList.get(i)
• second aList.get(j)
• aList.remove(i)
• aList.add(i, second)
• aList.remove(j)
• aList.add(j, first)
• // end Swap

26
q2 solution - alternative

• void swap(List aList, int i, int j) throws
  ListOutOfBoundsException
• // ----------------------------------------------
  ---------
• // Swaps the ith and the jth items in the list
  aList.
• // Precondition aList is a list of type
  Object.
• // Postconditions The ith and jth items are
  swapped in aList
• // ----------------------------------------------
  ---------
• Object first, second
• first aList.get(i)
• second aList.get(j)
• aList.set(i, second)
• aList.set(j, first)
• // end Swap

27
q3

• Use the method swap that you wrote in Question 2
  to write a method that reverses the order of the
  items in a list aList.

28
q3 solution

• void reverseList(ListReferenceBased aList) throws
  
• ListOutOfBoundsException
• // ----------------------------------------------
  --------
• // Reverses the order of the items in list
  aList.
• // Preconditions none.
• // Postconditions The contents of aList are in
  reverse order.
• // ----------------------------------------------
  --------
• int high aList.size()
• for(int low 1 low lt high low, high--)
• swap(aList, low, high)
• // end ReverseList

29
q4 q5

• Identify the operations in an ADT.
• If you are writing the ADT to manage some data,
  what are the operations you need?

30
q4

• In mathematics, a set is a group of distinct
  items. Specify operations as a part of the ADT
  set.

31
q4 solution

• Some ADT Set operations (Operate on this set)
• createSet() // creates an empty set
• isEmpty() // Is "this" set empty?
• setSize() // returns the no. of elements of
  "this" set
• isSubsetOf(set2) // Is set2 a subset of this
  set?
• isAnElement(item) // Is Item an element of
  this set?
• setUnion(set2) // union of set2 and this set
  
• setIntersection(set2) // intersection of set2
  and this set
• isMemberOf (item) // Is item a member of set
• isProperSubsetOf (set2) // Is set2 a proper
  subset of this set ?
• setEqual (set2) // Is set 2 equal
  to this set?
• setDifference (set2) // return the set
  difference btwn two sets
• addElement (item) // Insert an element into
  the set

32
q5

• Specify operations that are as part of the ADT
  Fraction. Include typical operations such as
  addition, subtraction and reduce (reduce fraction
  to lowest terms).

33
q5 solution

• Some ADT Fraction operations
• createFraction() // creates a fraction with a
  value of 0
• createFraction(num, denom) // creates fraction
  num/denom
• setFraction(num, denom) // sets fraction
  num/denom
• getNumerator() // returns the fraction's
  numerator
• getDenominator() // returns the fraction's
  denominator
• addFraction(secondFraction) // returns the sum
• subtractFraction(secondFraction)// returns the
  difference
• multiplyFraction(secondFraction) // returns the
  product
• divideFraction(secondFraction) // returns the
  quotient
• reduceToLowestTerms() // Reduce numerator and
  denominator
• // to lowest terms

34
q6

• Implement ADT Set that you proposed in Q4 using
  ArrayList of Integers.
• Think of the algorithm before you implement it!

35
q6

• addElement(Integer o)
• Add an integer into the set only if the set does
  not already have the element
• isSubsetOf(Set s2)
• How do you check that set s2 is a subset of the
  current set ?

36
q6 solution (1)

• import java.util.
• public class Set
• private ArrayList ltIntegergt v
• public Set () v new ArrayList ltIntegergt ()
  
• // addElement into this set
• public void addElement (Integer o) if
  (!v.contains (o)) v.add (o)
• // determines whether this Set is empty
• public boolean isEmpty() return (v.size ()
  0)
• // returns the number of elements in this Set
  (the cardinality)
• public int setSize() return v.size ()

37
q6 solution (2)

• // determines whether set2 is a subSet of this
  set
• public boolean isSubsetOf(Set set2)
• boolean subset true
• int i 0
• while (subset i lt set2.v.size())
• if (!v.contains (set2.v.get (i)))
  subset false
• return subset
• // determines if Item is an element of this
  set
• public boolean isAnElement(Integer item)
• return v.contains (item)

38
q6 solution (3)

• // inserts all items in set2 not in this set
  into this set
• public void setUnion(Set set2)
• for (int i 0 i lt set2.v.size() i)
• if (!v.contains (set2.v.get (i))) v.add
  (set2.v.get (i))
• // this set will contain common elements of
  this set and set2
• public void setIntersection(Set set2)
• ArrayList ltIntegergt temp new ArrayList
  ltIntegergt ()
• for (int i 0 i lt v.size () i)
• if (set2.v.contains (v.get (i))) temp.add
  (v.get (i))
• v new ArrayList ltIntegergt ()
• for (int i 0 i lt temp.size () i) v.add
  (temp.get (i))