Mega Code Archive
This class implements the heap interface using a java util List as the underlying data structure
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///////////////////////////////////////////////////////////////////////////////
//Copyright (C) 2005 Thomas Morton
//
//This library is free software; you can redistribute it and/or
//modify it under the terms of the GNU Lesser General Public
//License as published by the Free Software Foundation; either
//version 2.1 of the License, or (at your option) any later version.
//
//This library is distributed in the hope that it will be useful,
//but WITHOUT ANY WARRANTY; without even the implied warranty of
//MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
//GNU Lesser General Public License for more details.
//
//You should have received a copy of the GNU Lesser General Public
//License along with this program; if not, write to the Free Software
//Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
//////////////////////////////////////////////////////////////////////////////
//package opennlp.tools.util;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;
/**
* This class implements the heap interface using a {@link java.util.List} as the underlying
* data structure. This heap allows values which are equals to be inserted. The heap will
* return the top K values which have been added where K is specified by the size passed to
* the constructor. K+1 values are not gaurenteed to be kept in the heap or returned in a
* particular order.
*/
public class ListHeap implements Heap {
private List list;
private Comparator comp;
private int size;
private Object max = null;
/**
* Creates a new heap with the specified size using the sorted based on the
* specified comparator.
* @param sz The size of the heap.
* @param c The comparator to be used to sort heap elements.
*/
public ListHeap(int sz, Comparator c) {
size = sz;
comp = c;
list = new ArrayList(sz);
}
/**
* Creates a new heap of the specified size.
* @param sz The size of the new heap.
*/
public ListHeap(int sz) {
this(sz, null);
}
private int parent(int i) {
return (i - 1) / 2;
}
private int left(int i) {
return (i + 1) * 2 - 1;
}
private int right(int i) {
return (i + 1) * 2;
}
public int size() {
return list.size();
}
private void swap(int x, int y) {
Object ox = list.get(x);
Object oy = list.get(y);
list.set(y, ox);
list.set(x, oy);
}
private boolean lt(Object o1, Object o2) {
if (comp != null) {
return comp.compare(o1, o2) < 0;
}
else {
return ((Comparable) o1).compareTo(o2) < 0;
}
}
private boolean gt(Object o1, Object o2) {
if (comp != null) {
return comp.compare(o1, o2) > 0;
}
else {
return ((Comparable) o1).compareTo(o2) > 0;
}
}
private void heapify(int i) {
while (true) {
int l = left(i);
int r = right(i);
int smallest;
if (l < list.size() && lt(list.get(l), list.get(i)))
smallest = l;
else
smallest = i;
if (r < list.size() && lt(list.get(r), list.get(smallest)))
smallest = r;
if (smallest != i) {
swap(smallest, i);
i = smallest;
}
else
break;
}
}
public Object extract() {
if (list.size() == 0) {
throw new RuntimeException("Heap Underflow");
}
Object top = list.get(0);
int last = list.size() - 1;
if (last != 0) {
list.set(0, list.remove(last));
heapify(0);
}
else {
list.remove(last);
}
return top;
}
public Object first() {
if (list.size() == 0) {
throw new RuntimeException("Heap Underflow");
}
return list.get(0);
}
public Object last() {
if (list.size() == 0) {
throw new RuntimeException("Heap Underflow");
}
return max;
}
public void add(Object o) {
/* keep track of max to prevent unnecessary insertion */
if (max == null) {
max = o;
}
else if (gt(o, max)) {
if (list.size() < size) {
max = o;
}
else {
return;
}
}
list.add(o);
int i = list.size() - 1;
//percolate new node to correct position in heap.
while (i > 0 && gt(list.get(parent(i)), o)) {
list.set(i, list.get(parent(i)));
i = parent(i);
}
list.set(i, o);
}
public void clear() {
list.clear();
}
public Iterator iterator() {
return list.iterator();
}
public boolean isEmpty() {
return this.list.isEmpty();
}
public static void main(String[] args) {
Heap heap = new ListHeap(5);
for (int ai=0;ai<args.length;ai++){
heap.add(Integer.valueOf(Integer.parseInt(args[ai])));
}
while (!heap.isEmpty()) {
System.out.print(heap.extract()+" ");
}
System.out.println();
}
}
///////////////////////////////////////////////////////////////////////////////
//Copyright (C) 2003 Thomas Morton
//
//This library is free software; you can redistribute it and/or
//modify it under the terms of the GNU Lesser General Public
//License as published by the Free Software Foundation; either
//version 2.1 of the License, or (at your option) any later version.
//
//This library is distributed in the hope that it will be useful,
//but WITHOUT ANY WARRANTY; without even the implied warranty of
//MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
//GNU Lesser General Public License for more details.
//
//You should have received a copy of the GNU Lesser General Public
//License along with this program; if not, write to the Free Software
//Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
//////////////////////////////////////////////////////////////////////////////
/** Interface for interacting with a Heap data structure.
* This implementation extract objects from smallest to largest based on either
* their natural ordering or the comparator provided to an implementation.
* While this is a typical of a heap it allows this objects natural ordering to
* match that of other sorted collections.
* */
interface Heap {
/**
* Removes the smallest element from the heap and returns it.
* @return The smallest element from the heap.
*/
public Object extract();
/**
* Returns the smallest element of the heap.
* @return The top element of the heap.
*/
public Object first();
/**
* Returns the largest element of the heap.
* @return The largest element of the heap.
*/
public Object last();
/**
* Adds the specified object to the heap.
* @param o The object to add to the heap.
*/
public void add(Object o);
/**
* Returns the size of the heap.
* @return The size of the heap.
*/
public int size();
/**
* Returns whether the heap is empty.
* @return true if the heap is empty; false otherwise.
*/
public boolean isEmpty();
/**
* Returns an iterator over the elements of the heap. No specific ordering of these
* elements is guaranteed.
* @return An iterator over the elements of the heap.
*/
public Iterator iterator();
/**
* Clears the contents of the heap.
*/
public void clear();
}
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