Package squidpony.squidmath

Class IntSet

java.lang.Object
squidpony.squidmath.IntSet
All Implemented Interfaces:
Serializable
public class IntSet
extends Object
implements Serializable
An unordered set where the items are unboxed ints. No allocation is done except when growing the table size.

This class performs fast contains and remove (typically O(1), worst case O(n) but that is rare in practice). Add may be slightly slower, depending on hash collisions. Hashcodes are rehashed to reduce collisions and the need to resize. Load factors greater than 0.91 greatly increase the chances to resize to the next higher POT size.

Unordered sets and maps are not designed to provide especially fast iteration. Iteration is faster with OrderedSet, OrderedMap, and for primitive-valued keys, IntIntOrderedMap and IntDoubleOrderedMap.

This implementation uses linear probing with the backward shift algorithm for removal. Hashcodes are rehashed using Fibonacci hashing, instead of the more common power-of-two mask, to better distribute poor hashCodes (see Malte Skarupke's blog post). Linear probing continues to work even when all hashCodes collide, just more slowly.
This class is based on libGDX 1.9.11-SNAPSHOT's IntSet class, and fully replaces the older ShortSet class within SquidLib's usage. Porting older code that uses ShortSet should be a little easier due to the addAll(short[]) and random(IRNG) methods. ShortSet used the somewhat-problematic cuckoo-hashing technique, where this uses the more standard linear probing (like OrderedSet).

Author:
Nathan Sweet, Tommy Ettinger
See Also:
Serialized Form

  • Nested Class Summary

    Nested Classes 
    Modifier and Type Class Description
    static class  IntSet.IntSetIterator  

  • Field Summary

    Fields 
    Modifier and Type Field Description
    protected int mask
    A bitmask used to confine hashcodes to the size of the table.
    protected int shift
    Used by place(int) to bit shift the upper bits of a long into a usable range (>= 0 and <= mask).
    int size  

  • Constructor Summary

    Constructors 
    Constructor Description
    IntSet()
    Creates a new set with an initial capacity of 51 and a load factor of 0.8.
    IntSet​(int initialCapacity)
    Creates a new set with a load factor of 0.8.
    IntSet​(int initialCapacity, float loadFactor)
    Creates a new set with the specified initial capacity and load factor.
    IntSet​(IntSet set)
    Creates a new set identical to the specified set.

  • Method Summary

    Modifier and Type Method Description
    boolean add​(int key)
    Returns true if the key was not already in the set.
    void addAll​(int... array)  
    void addAll​(int[] array, int offset, int length)  
    void addAll​(short[] array)  
    void addAll​(short[] array, int offset, int length)  
    void addAll​(IntSet set)  
    void addAll​(IntVLA array)  
    void addAll​(IntVLA array, int offset, int length)  
    IntVLA appendInto​(IntVLA array)
    Appends to an existing (non-null) IntVLA with all the int items in this IntSet.
    void clear()  
    void clear​(int maximumCapacity)
    Clears the set and reduces the size of the backing arrays to be the specified capacity / loadFactor, if they are larger.
    boolean contains​(int key)  
    void ensureCapacity​(int additionalCapacity)
    Increases the size of the backing array to accommodate the specified number of additional items / loadFactor.
    boolean equals​(Object obj)  
    int first()  
    int hashCode()  
    boolean isEmpty()
    Returns true if the set is empty.
    IntSet.IntSetIterator iterator()
    Returns an iterator for the keys in the set.
    boolean notEmpty()
    Returns true if the set has one or more items.
    protected int place​(int item)
    Returns an index between 0 (inclusive) and mask (inclusive) for the specified item.
    int random​(IRNG rng)
    Gets a random int from this IntSet, using the given IRNG to generate random values.
    boolean remove​(int key)
    Returns true if the key was removed.
    void shrink​(int maximumCapacity)
    Reduces the size of the backing arrays to be the specified capacity / loadFactor, or less.
    int[] toArray()
    Allocates a new in array and fills it with the contents of this IntSet.
    int[] toArray​(int[] array)
    Fills an existing (non-null) int array with as many items from this IntSet as will fit in the array, until either the array is full or the IntSet has no more items to offer.
    String toString()  
    static IntSet with​(int... array)  
    static IntSet with​(IntVLA array)  

    Methods inherited from class java.lang.Object

    clone, finalize, getClass, notify, notifyAll, wait, wait, wait

  • Field Details

    • size

      public int size

    • shift

      protected int shift
      Used by place(int) to bit shift the upper bits of a long into a usable range (>= 0 and <= mask). The shift can be negative, which is convenient to match the number of bits in mask: if mask is a 7-bit number, a shift of -7 shifts the upper 7 bits into the lowest 7 positions. This class sets the shift > 32 and < 64, which if used with an int will still move the upper bits of an int to the lower bits due to Java's implicit modulus on shifts.

      mask can also be used to mask the low bits of a number, which may be faster for some hashcodes, if place(int) is overridden.

    • mask

      protected int mask
      A bitmask used to confine hashcodes to the size of the table. Must be all 1 bits in its low positions, ie a power of two minus 1. If place(int) is overriden, this can be used instead of shift to isolate usable bits of a hash.

  • Constructor Details

    • IntSet

      public IntSet()
      Creates a new set with an initial capacity of 51 and a load factor of 0.8.

    • IntSet

      public IntSet​(int initialCapacity)
      Creates a new set with a load factor of 0.8.
      Parameters:
      initialCapacity - If not a power of two, it is increased to the next nearest power of two.

    • IntSet

      public IntSet​(int initialCapacity, float loadFactor)
      Creates a new set with the specified initial capacity and load factor. This set will hold initialCapacity items before growing the backing table.
      Parameters:
      initialCapacity - If not a power of two, it is increased to the next nearest power of two.

    • IntSet

      public IntSet​(IntSet set)
      Creates a new set identical to the specified set.

  • Method Details

    • place

      protected int place​(int item)
      Returns an index between 0 (inclusive) and mask (inclusive) for the specified item.

      The default implementation uses Fibonacci hashing on the item's Object.hashCode(): the hashcode is multiplied by a long constant (2 to the 64th, divided by the golden ratio) then the uppermost bits are shifted into the lowest positions to obtain an index in the desired range. Multiplication by a long may be slower than int (eg on GWT) but greatly improves rehashing, allowing even very poor hashcodes, such as those that only differ in their upper bits, to be used without high collision rates. Fibonacci hashing has increased collision rates when all or most hashcodes are multiples of larger Fibonacci numbers (see Malte Skarupke's blog post).

      This method can be overriden to customizing hashing. This may be useful eg in the unlikely event that most hashcodes are Fibonacci numbers, if keys provide poor or incorrect hashcodes, or to simplify hashing if keys provide high quality hashcodes and don't need Fibonacci hashing: return item.hashCode() & mask;

    • add

      public boolean add​(int key)
      Returns true if the key was not already in the set.

    • addAll

      public void addAll​(IntVLA array)

    • addAll

      public void addAll​(IntVLA array, int offset, int length)

    • addAll

      public void addAll​(int... array)

    • addAll

      public void addAll​(int[] array, int offset, int length)

    • addAll

      public void addAll​(short[] array)

    • addAll

      public void addAll​(short[] array, int offset, int length)

    • addAll

      public void addAll​(IntSet set)

    • remove

      public boolean remove​(int key)
      Returns true if the key was removed.

    • notEmpty

      public boolean notEmpty()
      Returns true if the set has one or more items.

    • isEmpty

      public boolean isEmpty()
      Returns true if the set is empty.

    • shrink

      public void shrink​(int maximumCapacity)
      Reduces the size of the backing arrays to be the specified capacity / loadFactor, or less. If the capacity is already less, nothing is done. If the set contains more items than the specified capacity, the next highest power of two capacity is used instead.

    • clear

      public void clear​(int maximumCapacity)
      Clears the set and reduces the size of the backing arrays to be the specified capacity / loadFactor, if they are larger.

    • clear

      public void clear()

    • contains

      public boolean contains​(int key)

    • first

      public int first()

    • random

      public int random​(IRNG rng)
      Gets a random int from this IntSet, using the given IRNG to generate random values. If this IntSet is empty, throws an UnsupportedOperationException. This method operates in linear time, unlike the random item retrieval methods in OrderedSet and OrderedMap, which take constant time.
      Parameters:
      rng - an IRNG, such as RNG or GWTRNG
      Returns:
      a random int from this IntSet

    • ensureCapacity

      public void ensureCapacity​(int additionalCapacity)
      Increases the size of the backing array to accommodate the specified number of additional items / loadFactor. Useful before adding many items to avoid multiple backing array resizes.

    • hashCode

      public int hashCode()
      Overrides:
      hashCode in class Object

    • equals

      public boolean equals​(Object obj)
      Overrides:
      equals in class Object

    • toString

      public String toString()
      Overrides:
      toString in class Object

    • iterator

      public IntSet.IntSetIterator iterator()
      Returns an iterator for the keys in the set. Remove is supported.

      The same iterator instance is returned each time this method is called. Use the IntSet.IntSetIterator constructor for nested or multithreaded iteration.

    • with

      public static IntSet with​(int... array)

    • with

      public static IntSet with​(IntVLA array)

    • toArray

      public int[] toArray()
      Allocates a new in array and fills it with the contents of this IntSet.
      Returns:
      a new int array containing all the int items of this IntSet.

    • toArray

      public int[] toArray​(int[] array)
      Fills an existing (non-null) int array with as many items from this IntSet as will fit in the array, until either the array is full or the IntSet has no more items to offer.
      Parameters:
      array - a non-null int array; can have a length that is the same as, more than or less than size
      Returns:
      array, after adding items from this

    • appendInto

      public IntVLA appendInto​(IntVLA array)
      Appends to an existing (non-null) IntVLA with all the int items in this IntSet.
      Parameters:
      array - a non-null IntVLA; no items will be removed, and the contents of this will be added at the end
      Returns:
      array, after adding items from this