Package org.jheaps.tree

Class ReflectedHeap<K,​V>

  • Type Parameters:
    K - the type of keys maintained by this heap
    V - the type of values maintained by this heap
    All Implemented Interfaces:
    java.io.Serializable, AddressableHeap<K,​V>, DoubleEndedAddressableHeap<K,​V>, MergeableDoubleEndedAddressableHeap<K,​V>
    Direct Known Subclasses:
    ReflectedFibonacciHeap, ReflectedPairingHeap
    public class ReflectedHeap<K,​V>
extends java.lang.Object
implements MergeableDoubleEndedAddressableHeap<K,​V>, java.io.Serializable
    Reflected double ended heaps. The heap is sorted according to the natural ordering of its keys, or by a Comparator provided at heap creation time, depending on which constructor is used.

    This class implements a general technique which uses two MergeableAddressableHeaps to implement a double ended heap, described in detail in the following paper:

    • C. Makris, A. Tsakalidis, and K. Tsichlas. Reflected min-max heaps. Information Processing Letters, 86(4), 209--214, 2003.

    The running time bounds depend on the implementation of the underlying used heap. All the above bounds, however, assume that the user does not perform cascading melds on heaps such as: 

     d.meld(e);
 c.meld(d);
 b.meld(c);
 a.meld(b);
    The above scenario, although efficiently supported by using union-find with path compression, invalidates the claimed bounds.

    Note that the ordering maintained by a this heap, like any heap, and whether or not an explicit comparator is provided, must be consistent with equals if this heap is to correctly implement the AddressableHeap interface. (See Comparable or Comparator for a precise definition of consistent with equals.) This is so because the AddressableHeap interface is defined in terms of the equals operation, but this heap performs all key comparisons using its compareTo (or compare) method, so two keys that are deemed equal by this method are, from the standpoint of this heap, equal. The behavior of a heap is well-defined even if its ordering is inconsistent with equals; it just fails to obey the general contract of the AddressableHeap interface.

    Note that this implementation is not synchronized. If multiple threads access a heap concurrently, and at least one of the threads modifies the heap structurally, it must be synchronized externally. (A structural modification is any operation that adds or deletes one or more elements or changing the key of some element.) This is typically accomplished by synchronizing on some object that naturally encapsulates the heap.

    See Also:
    Serialized Form

    • Field Detail

      • comparator

        private final java.util.Comparator<? super K> comparator
        The comparator used to maintain order in this heap, or null if it uses the natural ordering of its keys.

      • size

        private long size
        Size of the heap

      • other

        private ReflectedHeap<K,​V> other
        Used to reference the current heap or some other heap in case of melding, so that handles remain valid even after a meld, without having to iterate over them. In order to avoid maintaining a full-fledged union-find data structure, we disallow a heap to be used in melding more than once. We use however, path-compression in case of cascading melds, that it, a handle moves from one heap to another and then another.

    • Constructor Detail

      • ReflectedHeap

        public ReflectedHeap​(AddressableHeapFactory<K,​?> heapFactory)
        Constructs a new, empty heap, using the natural ordering of its keys. All keys inserted into the heap must implement the Comparable interface. Furthermore, all such keys must be mutually comparable: k1.compareTo(k2) must not throw a ClassCastException for any keys k1 and k2 in the heap. If the user attempts to put a key into the heap that violates this constraint (for example, the user attempts to put a string key into a heap whose keys are integers), the insert(Object key) call will throw a ClassCastException.
        Parameters:
        heapFactory - a factory for the underlying heap implementation
        Throws:
        java.lang.NullPointerException - if the heap factory is null

      • ReflectedHeap

        public ReflectedHeap​(AddressableHeapFactory<K,​?> heapFactory,
                     java.util.Comparator<? super K> comparator)
        Constructs a new, empty heap, ordered according to the given comparator. All keys inserted into the heap must be mutually comparable by the given comparator: comparator.compare(k1, k2) must not throw a ClassCastException for any keys k1 and k2 in the heap. If the user attempts to put a key into the heap that violates this constraint, the insert(Object key) call will throw a ClassCastException.
        Parameters:
        heapFactory - a factory for the underlying heap implementation
        comparator - the comparator that will be used to order this heap. If null, the natural ordering of the keys will be used.
        Throws:
        java.lang.NullPointerException - if the heap factory is null