Class ObjectArrayIndirectPriorityQueue<K>

  • All Implemented Interfaces:
    IndirectPriorityQueue<K>

    public class ObjectArrayIndirectPriorityQueue<K>
    extends Object
    implements IndirectPriorityQueue<K>
    A type-specific array-based semi-indirect priority queue.

    Instances of this class use as reference list a reference array, which must be provided to each constructor, and represent a priority queue using a backing array of integer indices—all operations are performed directly on the array. The array is enlarged as needed, but it is never shrunk. Use the trim() method to reduce its size, if necessary.

    This implementation is extremely inefficient, but it is difficult to beat when the size of the queue is very small. Moreover, it allows to enqueue several time the same index, without limitations.

    • Constructor Detail

      • ObjectArrayIndirectPriorityQueue

        public ObjectArrayIndirectPriorityQueue​(K[] refArray,
                                                int capacity,
                                                Comparator<? super K> c)
        Creates a new empty queue without elements with a given capacity and comparator.
        Parameters:
        refArray - the reference array.
        capacity - the initial capacity of this queue.
        c - the comparator used in this queue, or null for the natural order.
      • ObjectArrayIndirectPriorityQueue

        public ObjectArrayIndirectPriorityQueue​(K[] refArray,
                                                int capacity)
        Creates a new empty queue with given capacity and using the natural order.
        Parameters:
        refArray - the reference array.
        capacity - the initial capacity of this queue.
      • ObjectArrayIndirectPriorityQueue

        public ObjectArrayIndirectPriorityQueue​(K[] refArray,
                                                Comparator<? super K> c)
        Creates a new empty queue with capacity equal to the length of the reference array and a given comparator.
        Parameters:
        refArray - the reference array.
        c - the comparator used in this queue, or null for the natural order.
      • ObjectArrayIndirectPriorityQueue

        public ObjectArrayIndirectPriorityQueue​(K[] refArray)
        Creates a new empty queue with capacity equal to the length of the reference array and using the natural order.
        Parameters:
        refArray - the reference array.
      • ObjectArrayIndirectPriorityQueue

        public ObjectArrayIndirectPriorityQueue​(K[] refArray,
                                                int[] a,
                                                int size,
                                                Comparator<? super K> c)
        Wraps a given array in a queue using a given comparator.

        The queue returned by this method will be backed by the given array.

        Parameters:
        refArray - the reference array.
        a - an array of indices into refArray.
        size - the number of elements to be included in the queue.
        c - the comparator used in this queue, or null for the natural order.
      • ObjectArrayIndirectPriorityQueue

        public ObjectArrayIndirectPriorityQueue​(K[] refArray,
                                                int[] a,
                                                Comparator<? super K> c)
        Wraps a given array in a queue using a given comparator.

        The queue returned by this method will be backed by the given array.

        Parameters:
        refArray - the reference array.
        a - an array of indices into refArray.
        c - the comparator used in this queue, or null for the natural order.
      • ObjectArrayIndirectPriorityQueue

        public ObjectArrayIndirectPriorityQueue​(K[] refArray,
                                                int[] a,
                                                int size)
        Wraps a given array in a queue using the natural order.

        The queue returned by this method will be backed by the given array.

        Parameters:
        refArray - the reference array.
        a - an array of indices into refArray.
        size - the number of elements to be included in the queue.
      • ObjectArrayIndirectPriorityQueue

        public ObjectArrayIndirectPriorityQueue​(K[] refArray,
                                                int[] a)
        Wraps a given array in a queue using the natural order.

        The queue returned by this method will be backed by the given array.

        Parameters:
        refArray - the reference array.
        a - an array of indices into refArray.
    • Method Detail

      • enqueue

        public void enqueue​(int x)
        Enqueues a new element.

        Note that for efficiency reasons this method will not throw an exception when x is already in the queue. However, the queue state will become inconsistent and the following behaviour will not be predictable.

        Specified by:
        enqueue in interface IndirectPriorityQueue<K>
        Parameters:
        x - the element to enqueue.
      • changed

        public void changed​(int index)
        Notifies this queue that the specified element has changed (optional operation).

        Note that the specified element must belong to this queue.

        This default implementation just throws an UnsupportedOperationException.

        Note that for efficiency reasons this method will not throw an exception when index is not in the queue.

        Specified by:
        changed in interface IndirectPriorityQueue<K>
        Parameters:
        index - the element that has changed.
      • remove

        public boolean remove​(int index)
        Description copied from interface: IndirectPriorityQueue
        Removes the specified element from this queue (optional operation).

        This default implementation just throws an UnsupportedOperationException.

        Specified by:
        remove in interface IndirectPriorityQueue<K>
        Parameters:
        index - the element to be removed.
        Returns:
        true if the index was in the queue.
      • front

        public int front​(int[] a)
        Writes in the provided array the front of the queue, that is, the set of indices whose elements have the same priority as the top.
        Specified by:
        front in interface IndirectPriorityQueue<K>
        Parameters:
        a - an array whose initial part will be filled with the frnot (must be sized as least as the heap size).
        Returns:
        the number of elements of the front.
      • size

        public int size()
        Description copied from interface: IndirectPriorityQueue
        Returns the number of elements in this queue.
        Specified by:
        size in interface IndirectPriorityQueue<K>
        Returns:
        the number of elements in this queue.
      • trim

        public void trim()
        Trims the backing array so that it has exactly size() elements.
      • comparator

        public Comparator<? super K> comparator()
        Description copied from interface: IndirectPriorityQueue
        Returns the comparator associated with this queue, or null if it uses its elements' natural ordering.
        Specified by:
        comparator in interface IndirectPriorityQueue<K>
        Returns:
        the comparator associated with this sorted set, or null if it uses its elements' natural ordering.