1 / 13

Listen, Stacks und Queues

Listen, Stacks und Queues. p. head. tail. x. Arrays statisch wahlfreier Zugriff. a 0. a 1. a 2. a i. a N-1. Linked Lists dynamisch sequentieller Zugriff. head. tail. Linked List in Java (1) class LinkedList { class Node { Object info; Node next;

veda-miles
Download Presentation

Listen, Stacks und Queues

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Helmut Schauer Educational Engineering Lab Department for Informatics University of Zurich • Listen, Stacks • und Queues p head tail x

  2. Helmut Schauer Educational Engineering Lab Department for Informatics University of Zurich • Arrays • statisch • wahlfreier Zugriff a0 a1 a2 ai aN-1

  3. Helmut Schauer Educational Engineering Lab Department for Informatics University of Zurich • Linked Lists • dynamisch • sequentieller Zugriff head tail

  4. Helmut Schauer Educational Engineering Lab Department for Informatics University of Zurich • Linked List in Java (1) • class LinkedList { • class Node { • Object info; • Node next; • Node(Object x) {info = x;} • } • Node head, tail; • LinkedList() {head = null; tail = null;} • boolean isEmpty() {return head == null;} • ... • }

  5. p head tail x Helmut Schauer Educational Engineering Lab Department for Informatics University of Zurich • Linked List in Java (2) • void insertFirst(Object x) { • Node p = new Node(x); • if (isEmpty()) tail = p; • else p.next = head; • head = p; • }

  6. p head tail x Helmut Schauer Educational Engineering Lab Department for Informatics University of Zurich • Linked List in Java (2) • Object removeFirst() { • if (isEmpty()) return null; • Node p = head; • head = p.next; • if (isEmpty()) tail = null; • return p.info; • }

  7. Helmut Schauer Educational Engineering Lab Department for Informatics University of Zurich • Linked List in Java (3) • void insertLast(Object x) { • if (isEmpty()) • insertFirst(x); • else { • Node p = new Node(x); • tail.next = p; • tail = p; • } • } tail davor: tail p danach:

  8. Helmut Schauer Educational Engineering Lab Department for Informatics University of Zurich • Linked List in Java (4) • int size() { • int count = 0; • for (Node p = head; p != null; p = p.next) • count++; • return count; • } • boolean contains(Object x) { • for (Node p = head; p != null; p = p.next) • if (p.info.equals(x)) return true; • return false; • }

  9. Helmut Schauer Educational Engineering Lab Department for Informatics University of Zurich • Adapter für String List • class StringList { • private LinkedList list; • StringList() {list = new LinkedList();} • boolean isEmpty() {return list.isEmpty();} • void insertFirst(String x) {list.insertFirst(x);} • String removeFirst() {return (String)list.removeFirst();} • ... • }

  10. Helmut Schauer Educational Engineering Lab Department for Informatics University of Zurich • Stack in Java • class Stack extends LinkedList { • Stack() {super();} • void push(Object x) {insertFirst(x);} • Object pop() {return removeFirst();} • Object top() { • if (isEmpty()) • return null; • else • return head.info; • } • }

  11. Helmut Schauer Educational Engineering Lab Department for Informatics University of Zurich • Ordered List in Java • class OrderedList extends LinkedList { • OrderedList() {super();} • void insert(Comparable x) { • if (isEmpty() || (x.compareTo((Comparable) head.info)<0)) • insertFirst(x); • else { • Node p = head; • while((p.next != null) && (x.compareTo((Comparable) p.next.info)>=0)) • p = p.next; • if (p.next == null) • insertLast(x); • else { • Node q = new Node(x); • q.next = p.next; • p.next = q; • } • } • } • }

  12. Helmut Schauer Educational Engineering Lab Department for Informatics University of Zurich • Assertions für Stacks • für jeden Stack s und jedes Objekt x muss gelten: • s = new Stack(); {s.size() = 0, s.isEmpty() = true} • {s.size() = n} s.push(x); {s.size() = n+1, s.isEmpty() = false} • s.push(x); {s.top() = x, s.pop() = x} • {P} s.push(x); s.pop(); {P}

  13. Helmut Schauer Educational Engineering Lab Department for Informatics University of Zurich • Assertions für Queues • für jede Queue q und jedes Objekt x muss gelten: • q = new Queue(); {q.size() = 0, q.isEmpty() = true} • {q.size() = n} q.put(x); {q.size() = n+1, q.isEmpty() = false} • ({Q, not q.isEmpty()} q.get(); q.put(x); {R}) impliziert • ({Q, not q.isEmpty()} q.put(x); q.get(); {R}) und umgekehrt

More Related