opennlp.tools.util.ListHeap Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
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 E 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) {
E ox = list.get(x);
E oy = list.get(y);
list.set(y, ox);
list.set(x, oy);
}
private boolean lt(E o1, E o2) {
if (comp != null) {
return comp.compare(o1, o2) < 0;
}
else {
return o1.compareTo(o2) < 0;
}
}
private boolean gt(E o1, E o2) {
if (comp != null) {
return comp.compare(o1, o2) > 0;
}
else {
return 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 E extract() {
if (list.size() == 0) {
throw new RuntimeException("Heap Underflow");
}
E 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 E first() {
if (list.size() == 0) {
throw new RuntimeException("Heap Underflow");
}
return list.get(0);
}
public E last() {
if (list.size() == 0) {
throw new RuntimeException("Heap Underflow");
}
return max;
}
public void add(E 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();
}
}