Package org.jheaps.monotone

Class BigIntegerRadixHeap

java.lang.Object
org.jheaps.monotone.BigIntegerRadixHeap
All Implemented Interfaces:
Serializable, Heap<BigInteger>
public class BigIntegerRadixHeap extends Object
A radix heap for BigInteger keys. The heap stores BigInteger keys sorted according to the natural ordering of its keys. A radix heap is a monotone heap, especially designed for algorithms (such as Dijkstra) which scan elements in order of nondecreasing keys.

The implementation uses arrays in order to store the elements. Operations insert and findMin are worst-case constant time. The cost of operation deleteMin is amortized O(logC) assuming the radix-heap contains keys in the range [0, C] or equivalently [a,a+C].

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.

Author:
Dimitrios Michail
See Also:

  • Field Details

    • EMPTY

      protected static final int EMPTY
      Denotes that a key does not belong to a bucket
      See Also:

    • buckets

      protected List<BigInteger>[] buckets
      The buckets as lists. We use array-lists instead of linked-lists, to be cache friendly.

    • size

      protected long size
      Number of elements

    • lastDeletedKey

      protected BigInteger lastDeletedKey
      Last deleted key. This value is used to distribute elements in the buckets. Should be initialized with the minKey value.

    • currentMin

      protected BigInteger currentMin
      The current minimum value (cached)

    • currentMinBucket

      protected int currentMinBucket
      The current minimum value bucket (cached)

    • currentMinPos

      protected int currentMinPos
      The current minimum value position in bucket (cached)

    • minKey

      protected BigInteger minKey
      Minimum key allowed

    • maxKey

      protected BigInteger maxKey
      Maximum key allowed

  • Constructor Details

    • BigIntegerRadixHeap

      public BigIntegerRadixHeap(BigInteger minKey, BigInteger maxKey)
      Constructs a new heap which can store values between a minimum and a maximum key value (inclusive). It is important to use the smallest key range as the heap uses O(logC) where C=maxKey-minKey+1 buckets to store elements. Moreover, the operation deleteMin requires amortized O(logC) time.
      Parameters:
      minKey - the non-negative minimum key that this heap supports (inclusive)
      maxKey - the maximum key that this heap supports (inclusive)
      Throws:
      IllegalArgumentException - if the minimum key is negative
      IllegalArgumentException - if the maximum key is less than the minimum key

  • Method Details

    • compare

      protected int compare(BigInteger o1, BigInteger o2)
      Compares its two arguments for order. Returns a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second.
      Parameters:
      o1 - the first object to be compared.
      o2 - the second object to be compared.
      Returns:
      a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second.

    • msd

      protected int msd(BigInteger a, BigInteger b)
      Compute the most significant digit which is different in the binary representation of two values, or -1 if numbers are equal.
      Parameters:
      a - the first value
      b - the second value
      Returns:
      the most significant digit which is different or -1 if numbers are equal

    • findMin

      public BigInteger findMin()
      Find an element with the minimum key.
      Specified by:
      findMin in interface Heap<K>
      Returns:
      an element with the minimum key

    • insert

      public void insert(BigInteger key)
      Insert a key into the heap.
      Specified by:
      insert in interface Heap<K>
      Parameters:
      key - the key to insert
      Throws:
      IllegalArgumentException - if the key is null
      IllegalArgumentException - if the key is less than the minimum allowed key
      IllegalArgumentException - if the key is more than the maximum allowed key
      IllegalArgumentException - if the key is less than the last deleted key (or the minimum key allowed if no key has been deleted)

    • deleteMin

      public BigInteger deleteMin()
      Delete and return an element with the minimum key. If multiple such elements exists, only one of them will be deleted. The cost of this operation is amortized O(logC) assuming the heap contains keys in the range [0, C] or equivalently [a, a+C].
      Specified by:
      deleteMin in interface Heap<K>
      Returns:
      the deleted element with the minimum key

    • isEmpty

      public boolean isEmpty()
      Returns true if this heap is empty.
      Specified by:
      isEmpty in interface Heap<K>
      Returns:
      true if this heap is empty, false otherwise

    • size

      public long size()
      Returns the number of elements in this heap.
      Specified by:
      size in interface Heap<K>
      Returns:
      the number of elements in this heap

    • clear

      public void clear()
      Clear all the elements of this heap.
      Specified by:
      clear in interface Heap<K>

    • comparator

      public Comparator<? super BigInteger> comparator()
      Always returns null since this heap uses the natural ordering of its keys.
      Specified by:
      comparator in interface Heap<K>
      Returns:
      null since this heap uses the natural ordering of its keys

    • computeBucket

      protected int computeBucket(BigInteger key, BigInteger minKey)
      Compute the bucket of a key based on a minimum key.
      Parameters:
      key - the key
      minKey - the minimum key
      Returns:
      the bucket where the key should go