Lista Ligada. Nó de Lista Ligada

Transcrição

1 Lista Ligada Estrutura com nós que armazenam elementos manter referências para elementos do início e fim da lista Operações Inserir: a seguir à posição corrente Remover: na posição corrente Pesquisar: por conteúdo ou por posição first last Listas - 1 package weiss.nonstandard; Nó de Lista Ligada // Basic node stored in a linked list // Note that this class is not accessible outside // of package weiss.nonstandard class ListNode public ListNode( Object theelement ) this( theelement, null ); public ListNode( Object theelement, ListNode n ) element = theelement; next = n; public Object element; public ListNode next; Listas - 2 Listas-1

2 Nós: inserção e remoção Nó da lista Class ListNode Object element; ListNode next; Inserir a seguir ao nó corrente tmp = new ListNode(); tmp.element = x; tmp.next = current.next; current.next = tmp; ou current.next = new ListNode(x, current.next); Apagar a seguir ao nó corrente current.next = current.next.next; Listas - 3 Nós cabeçalho e iteradores Nós de cabeçalho Usados para evitar tratar como casos especiais a inserção e remoção no primeiro lugar da lista Garantem que cada nó da lista tem sempre um nó anterior Percorrer a lista Aplicação manipula referências para nós da lista não pode garantir-se que as referências são válidas Lista mantém a posição corrente e acesso é por métodos garante-se consistência das referências só uma visita à lista Iteradores permitem manter posição corrente independente da lista Listas - 4 Listas-2

3 Nó de lista duplamente ligada * This is the doubly-linked list node. private static class Node public Node( Object d, Node p, Node n ) data = d; prev = p; next = n; public Object data; public Node prev; public Node next; Listas - 5 package weiss.util; * LinkedList class implements a doubly-linked list. public class LinkedList extends AbstractCollection implements List private static final Node NOT_FOUND = null; private int thesize; private Node beginmarker; private Node endmarker; private int modcount = 0; Listas - 6 Listas-3

4 * Construct an empty LinkedList. public LinkedList( ) clear( ); * Construct a LinkedList with same items as another Collection. public LinkedList( Collection other ) clear( ); Iterator itr = other.iterator( ); while( itr.hasnext( ) ) add( itr.next( ) ); Listas - 7 * Returns the number of items in this collection. the number of items in this collection. public int size( ) return thesize; * Tests if some item is in this collection. x any object. true if this collection contains an item equal to x. public boolean contains( Object x ) return findpos( x )!= NOT_FOUND; Listas - 8 Listas-4

5 * Returns the position of first item matching x in this collection, * or NOT_FOUND if not found. x any object. the position of first item matching x in this collection, * or NOT_FOUND if not found. private Node findpos( Object x ) for( Node p = beginmarker.next; p!= endmarker; p = p.next ) if( x == null ) if( p.data == null ) return p; else if( x.equals( p.data ) ) return p; return NOT_FOUND; Listas - 9 * Adds an item to this collection, at the end. public boolean add( Object x ) addlast( x ); return true; * Adds an item to this collection, at specified position. * Items at or after that position are slid one position higher. public void add( int idx, Object x ) Node p = getnode( idx ); Node newnode = new Node( x, p.prev, p ); newnode.prev.next = newnode; p.prev = newnode; thesize++; modcount++; Listas - 10 Listas-5

6 * Adds an item to this collection, at front. * Other items are slid one position higher. x any object. public void addfirst( Object x ) add( 0, x ); * Adds an item to this collection, at end. x any object. public void addlast( Object x ) add( size( ), x ); Listas - 11 * Returns the first item in the list. NoSuchElementException if the list is empty. public Object getfirst( ) if( isempty( ) ) throw new NoSuchElementException( ); return getnode( 0 ).data; * Returns the last item in the list. NoSuchElementException if the list is empty. public Object getlast( ) if( isempty( ) ) throw new NoSuchElementException( ); return getnode( size( ) - 1 ).data; Listas - 12 Listas-6

7 * Removes the first item in the list. the item was removed from the collection. NoSuchElementException if the list is empty. public Object removefirst( ) if( isempty( ) ) throw new NoSuchElementException( ); return remove( getnode( 0 ) ); * Removes the last item in the list. the item was removed from the collection. NoSuchElementException if the list is empty. public Object removelast( ) if( isempty( ) ) throw new NoSuchElementException( ); return remove( getnode( size( ) - 1 ) ); Listas - 13 * Removes an item from this collection. x any object. true if this item was removed from the collection. public boolean remove( Object x ) Node pos = findpos( x ); if( pos == NOT_FOUND ) return false; else remove( pos ); return true; * Returns the item at position idx. public Object get( int idx ) return getnode( idx ).data; Listas - 14 Listas-7

8 * Changes the item at position idx. idx the index to change. newval the new value. the old value. IndexOutOfBoundsException if index is out of range. public Object set( int idx, Object newval ) Node p = getnode( idx ); Object oldval = p.data; p.data = newval; return oldval; Listas - 15 * Gets the Node at position idx, which must range from 0 to size( ). private Node getnode( int idx ) Node p; if( idx < 0 idx > size( ) ) throw new IndexOutOfBoundsException( "getnode index: " + idx + "; size: " + size( ) ); if( idx < size( ) / 2 ) p = beginmarker.next; for( int i = 0; i < idx; i++ ) p = p.next; else p = endmarker; for( int i = size( ); i > idx; i-- ) p = p.prev; return p; Listas - 16 Listas-8

9 * Removes an item from this collection. idx the index of the object. the item was removed from the collection. public Object remove( int idx ) return remove( getnode( idx ) ); * Removes the object contained in Node p. p the Node containing the object. the item was removed from the collection. private Object remove( Node p ) p.next.prev = p.prev; p.prev.next = p.next; thesize--; modcount++; return p.data; Listas - 17 * Change the size of this collection to zero. public void clear( ) beginmarker = new Node( "BEGINMARKER", null, null ); endmarker = new Node( "ENDMARKER", beginmarker, null ); beginmarker.next = endmarker; thesize = 0; modcount++; Listas - 18 Listas-9

10 * Obtains an Iterator object used to traverse the collection. an iterator positioned prior to the first element. public Iterator iterator( ) return new LinkedListIterator( 0 ); * Obtains a ListIterator object used to traverse the collection bidirectionally. an iterator positioned prior to the requested element. idx the index to start the iterator. Use size() to do complete * reverse traversal. Use 0 to do complete forward traversal. public ListIterator listiterator( int idx ) return new LinkedListIterator( idx ); Listas - 19 LinkedListIterator private class LinkedListIterator implements ListIterator private Node current; private Node lastvisited = null; private boolean lastmovewasprev = false; private int expectedmodcount = modcount; public LinkedListIterator( int idx ) current = getnode( idx ); public boolean hasnext( ) if( expectedmodcount!= modcount ) throw new ConcurrentModificationException( ); return current!= endmarker; Listas - 20 Listas-10

11 LinkedListIterator public Object next( ) if(!hasnext( ) ) throw new NoSuchElementException( ); Object nextitem = current.data; lastvisited = current; current = current.next; lastmovewasprev = false; return nextitem; public boolean hasprevious( ) if( expectedmodcount!= modcount ) throw new ConcurrentModificationException( ); return current!= beginmarker.next; Listas - 21 LinkedListIterator public void remove( ) if( expectedmodcount!= modcount ) throw new ConcurrentModificationException( ); if( lastvisited == null ) throw new IllegalStateException( ); LinkedList.this.remove( lastvisited ); lastvisited = null; if( lastmovewasprev ) current = current.next; expectedmodcount++; Listas - 22 Listas-11

12 LinkedListIterator public Object previous( ) if( expectedmodcount!= modcount ) throw new ConcurrentModificationException( ); if(!hasprevious( ) ) throw new NoSuchElementException( ); current = current.prev; lastvisited = current; lastmovewasprev = true; return current.data; Listas - 23 Listas-12