Class PriorityQueue<T>

A PriorityQueue<T> maintains a partial ordering of its elements such that the element with least priority can always be found in constant time. Put()'s and Pop()'s require log(size) time.

NOTE: this class will pre-allocate a full array of length maxSize+1 if instantiated via the PriorityQueue(Int32, Boolean) constructor with prepopulate set to true. That maximum size can grow as we insert elements over the time.

This is a Lucene.NET INTERNAL API, use at your own risk

Inheritance

System.Object

PriorityQueue<T>

FieldValueHitQueue<T>

Namespace: Lucene.Net.Util

Assembly: Lucene.Net.dll

Syntax

public abstract class PriorityQueue<T> : object

Type Parameters

Name	Description
T

Constructors

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PriorityQueue(Int32)

Declaration

public PriorityQueue(int maxSize)

Parameters

Type	Name	Description
System.Int32	maxSize

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PriorityQueue(Int32, Boolean)

Declaration

public PriorityQueue(int maxSize, bool prepopulate)

Parameters

Type	Name	Description
System.Int32	maxSize
System.Boolean	prepopulate

Properties

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Count

Returns the number of elements currently stored in the PriorityQueue<T>. NOTE: This was size() in Lucene.

Declaration

public int Count { get; }

Property Value

Type	Description
System.Int32

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HeapArray

This method returns the internal heap array as T[].

This is a Lucene.NET INTERNAL API, use at your own risk

Declaration

protected T[] HeapArray { get; }

Property Value

Type	Description
T[]

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Top

Returns the least element of the PriorityQueue<T> in constant time. Returns null if the queue is empty.

Declaration

public T Top { get; }

Property Value

Type	Description
T

Methods

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Add(T)

Adds an Object to a PriorityQueue<T> in log(size) time. If one tries to add more objects than Lucene.Net.Util.PriorityQueue`1.maxSize from initialize and it is not possible to resize the heap, an is thrown.

Declaration

public T Add(T element)

Parameters

Type	Name	Description
T	element

Returns

Type	Description
T	The new 'top' element in the queue.

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Clear()

Removes all entries from the PriorityQueue<T>.

Declaration

public void Clear()

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GetSentinelObject()

This method can be overridden by extending classes to return a sentinel object which will be used by the PriorityQueue(Int32, Boolean) constructor to fill the queue, so that the code which uses that queue can always assume it's full and only change the top without attempting to insert any new object.

Those sentinel values should always compare worse than any non-sentinel value (i.e., LessThan(T, T) should always favor the non-sentinel values).

By default, this method returns false, which means the queue will not be filled with sentinel values. Otherwise, the value returned will be used to pre-populate the queue. Adds sentinel values to the queue.

If this method is extended to return a non-null value, then the following usage pattern is recommended:

// extends GetSentinelObject() to return a non-null value.
PriorityQueue<MyObject> pq = new MyQueue<MyObject>(numHits);
// save the 'top' element, which is guaranteed to not be null.
MyObject pqTop = pq.Top;
<...>
// now in order to add a new element, which is 'better' than top (after
// you've verified it is better), it is as simple as:
pqTop.Change().
pqTop = pq.UpdateTop();

NOTE: if this method returns a non-null value, it will be called by the PriorityQueue(Int32, Boolean) constructor Count times, relying on a new object to be returned and will not check if it's null again. Therefore you should ensure any call to this method creates a new instance and behaves consistently, e.g., it cannot return null if it previously returned non-null.

Declaration

protected virtual T GetSentinelObject()

Returns

Type	Description
T	The sentinel object to use to pre-populate the queue, or `null` if sentinel objects are not supported.

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InsertWithOverflow(T)

Adds an Object to a PriorityQueue<T> in log(size) time. It returns the object (if any) that was dropped off the heap because it was full. This can be the given parameter (in case it is smaller than the full heap's minimum, and couldn't be added), or another object that was previously the smallest value in the heap and now has been replaced by a larger one, or null if the queue wasn't yet full with Lucene.Net.Util.PriorityQueue`1.maxSize elements.

Declaration

public virtual T InsertWithOverflow(T element)

Parameters

Type	Name	Description
T	element

Returns

Type	Description
T

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LessThan(T, T)

Determines the ordering of objects in this priority queue. Subclasses must define this one method.

Declaration

protected abstract bool LessThan(T a, T b)

Parameters

Type	Name	Description
T	a
T	b

Returns

Type	Description
System.Boolean	`true` if parameter `a` is less than parameter `b`.

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Pop()

Removes and returns the least element of the PriorityQueue<T> in log(size) time.

Declaration

public T Pop()

Returns

Type	Description
T

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UpdateTop()

Should be called when the Object at top changes values. Still log(n) worst case, but it's at least twice as fast to

pq.Top.Change();
pq.UpdateTop();

instead of

o = pq.Pop();
o.Change();
pq.Push(o);

Declaration

public T UpdateTop()

Returns

Type	Description
T	The new 'top' element.