Doubly LinkedList is Symmetrical! LinkedList Efficiency. Monday, April 8, 13. insert insert remove remove remove walk

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1 How Can We Improve the State of Experimental Evaluation in Computer Siene Peter Sweeney IBM Researh, TJ Watson Friday, April 12, 12:00 Kendade Doubly LinkedList is Symmetrial! insert insert remove remove remove walk at front O(1) after O(1) at front O(1) after O(1) forward O(n) at end O(1) before O(1) at end O(1) before O(1) node O(1) bakward O(n) 2 LinkedList Effiieny O(1) O(n) O(1) O(n) How muh is the speed of eah method dependent on the number of elements in the linked list? int size() String get (int position); String set (int position, String value); boolean add (int value); void add (int position, String value); String remove (int position); 3

2 Walking a list with a For Loop int sumall (LinkedList<Integer> l) { int sum = 0; // Get an iterator for the list // While not at the end of the list for (int i = 0; i < l.size(); i++) { // Add in the next value sum = sum + l.get(i); return sum; What is the ost of get? What is the ost of sumall? 4 Iterator Interfae List interfae delares: publi Iterator<E> iterator() interfae Iterator<E> { // Return true if there are more entries left to visit in the list. publi boolean hasnext(); // Return the next entry in the list. publi E next(); // Remove the last entry that was returned by next. publi void remove(); hasnext() and next() behave similarly to the Sanner methods with the same names 5 Implementing the Iterator Interfae lass MyIterator<E> { private List<E> list; private Node<E> nextitem; private Node<E> previtem; publi MyIterator<E>() { publi boolean hasnext() { publi E next() { publi void remove() { previtem = null nextitem list 6

3 Implementing the Iterator Interfae Iterator<Integer> iter = list.iterator(); previtem = null nextitem list iter.next(); Implementing the Iterator Interfae publi E next() { previtem = null nextitem list 8 Implementing the Iterator Interfae publi boolean hasnext() { previtem = null nextitem list 9

4 Walking a list with an Iterator int sumall (List<Integer> l) { int sum = 0; // Get an iterator for the list Iterator<Integer> iter = l.iterator(); // While not at the end of the list while (iter.hasnext()) { // Add in the next value sum = sum + iter.next(); return sum; Using an iterator, what is the O() time of sumall? 10 Colletions Hierarhy <<interfae>> Iterable <<interfae>> Colletion <<interfae>> Queue <<interfae>> List <<abstrat>> AbstratColletion <<abstrat>> AbstratList ArrayList LinkedList Stak 11 Iterable ontains: publi Iterator<T> iterator(); 12

5 Colletion adds: publi boolean add (E value); publi void lear(); publi boolean ontains (Objet o); publi boolean isempty(); publi boolean remove (Objet o); publi int size(); - Holds multiple values - Size an grow as needed 13 List adds: publi boolean add (int index, E value); publi E get (int index); publi int indexof (Objet o); publi int lastindexof (Objet o); publi ListIterator<E> listiterator(); publi ListIterator<E> listiterator(int index); publi E remove (int index); publi E set (int index, E value); List<E> sublist(int fromindex, int toindex); - Ability to aess values by position 14 AbstratList provides method bodies for: publi boolean add (E value); publi void lear(); publi void addall(int index, Colletion<? extends E> ) publi Iterator<E> iterator(); publi ListIterator<E> listiterator(); publi ListIterator<E> listiterator(int index); publi List<E> sublist(int fromindex, int toindex); publi boolean equals (Objet o); publi int hashcode(); - Defines methods that behave the same for all implementations of List. 15

6 AbstratList s implementation of add publi boolean add(e e) { add(size(), e); return true; 16 ArrayList provides remaining method bodies and defines: publi ArrayList(); publi ArrayList(Colletion<E> ); publi ArrayList (int initialcapaity); publi int size(); publi int indexof (Objet o); publi int lastindexof (Objet o); publi E get (int index) publi void set (int index, E element) publi void add(int index, E element) publi E remove(int index)... - Defines the array-based representation 17 LinkedList provides remaining method bodies and defines: publi LinkedList(); publi LinkedList(Colletion<E> ); publi void addfirst (E value); publi void addlast (E value); publi Iterator<E> desendingiterator(); publi E getfirst(); publi E getlast(); publi E removefirst(); publi boolean removefirstourrene(objet o); publi E removelast(); publi boolean removelastourrene(objet o);... - Defines the linked list representation 18

7 Reversing a String Let s write a method to reverse the letters in a String. Example: reverse( at ) should return ta. at at t t ta ta a t a a 19 Stak Data struture that only allows aess to the last item added to it. lass Stak<E> { // Add item to end publi E push (E item) { // Get last item added publi E peek() { // Remove last item added publi E pop() { // Is it empty? publi boolean empty() { // How many items are in it? publi int size() { 20 Rewriting String Reversal String reverse (String s) {! Stak<Charater> letters = new Stak<Charater>();! for (int i = 0; i < s.length(); i++) {!! letters.push(s.harat(i));!!! String reversed = ;! while (!letters.isempty()) {!! reversed = reversed + letters.pop();!! return reversed; 21

8 Stak Implementation private LinkedList<E> values = new LinkedList<E>(); publi E push (E item) { values.add(item); return item; What is the O()? publi E peek() { if (values.isempty()) { throw new EmptyStakExeption(); return values.getlast(); a t 22 Implementing a Stak publi E pop() { if (values.isempty()) { throw new EmptyStakExeption(); return values.removelast(); What is the O()? publi boolean empty () { return values.isempty(); publi int size() { return values.size(); 23 Balaned Parentheses () is balaned ()() is balaned (()) is balaned (() is not balaned How do we write a method that takes a string parameter and returns true if the parentheses in the string are balaned? 24

9 ! publi boolean isbalaned (String str) {!! int numopen = 0;!! for (int i = 0; i < str.length(); i++) {!!! har nextchar = str.harat(i);!!! if (nextchar == '(') {!!!! numopen++;!!!!!! else if (nextchar == ')') {!!!! numopen--;!!!! if (numopen < 0) {!!!!! return false;!!!!!!!!!!!!! return numopen == 0;! 25 Balaned Parentheses - More than 1 Type of Parenthesis () is balaned ()[] is balaned ([]) is balaned ([)] is not balaned How do we write a method that takes a string parameter and returns true if the parentheses in the string are balaned? 26 publi boolean isbalaned (String str) { for eah harater in str { if it is an open paren { push the har onto a stak else if it is a lose paren { pop har off stak if popped har is not open for this har { return false; if stak is empty { return true; return false; 27

10 Stak adds push, pop, peek 28 Stak Traes Exeption in thread "AWT-EventQueue-0" java.lang.nullpointerexeption! at model.profile.addfriend(profile.java:85)! at gui.faepamphlet.addfriend(faepamphlet.java:219)! at gui.faepamphlet.ationperformed(faepamphlet.java:184)! at javax.swing.jcombobox.fireationevent(jcombobox.java:1197)! at javax.swing.jcombobox.setseleteditem(jcombobox.java:561)! at javax.swing.jcombobox.setseletedindex(jcombobox.java:597) (more omitted) Top of the stak identifies the method where the exeption ourred 2 nd item on the stak identifiers where the top method was alled And so on Call stak Variables in seleted ativation reord Text Current instrution 30

11 Call stak Variables in seleted ativation reord Current instrution 31