org.apache.lucene.util.collections.IntHashSet Maven / Gradle / Ivy
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package org.apache.lucene.util.collections;
import java.util.Arrays;
/**
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/**
* A Set or primitive int. Implemented as a HashMap of int->int. *
*
* @lucene.experimental
*/
public class IntHashSet {
// TODO (Facet): This is wasteful as the "values" are actually the "keys" and
// we could spare this amount of space (capacity * sizeof(int)). Perhaps even
// though it is not OOP, we should re-implement the hash for just that cause.
/**
* Implements an IntIterator which iterates over all the allocated indexes.
*/
private final class IndexIterator implements IntIterator {
/**
* The last used baseHashIndex. Needed for "jumping" from one hash entry
* to another.
*/
private int baseHashIndex = 0;
/**
* The next not-yet-visited index.
*/
private int index = 0;
/**
* Index of the last visited pair. Used in {@link #remove()}.
*/
private int lastIndex = 0;
/**
* Create the Iterator, make index point to the "first"
* index which is not empty. If such does not exist (eg. the map is
* empty) it would be zero.
*/
public IndexIterator() {
for (baseHashIndex = 0; baseHashIndex < baseHash.length; ++baseHashIndex) {
index = baseHash[baseHashIndex];
if (index != 0) {
break;
}
}
}
public boolean hasNext() {
return (index != 0);
}
public int next() {
// Save the last index visited
lastIndex = index;
// next the index
index = next[index];
// if the next index points to the 'Ground' it means we're done with
// the current hash entry and we need to jump to the next one. This
// is done until all the hash entries had been visited.
while (index == 0 && ++baseHashIndex < baseHash.length) {
index = baseHash[baseHashIndex];
}
return lastIndex;
}
public void remove() {
IntHashSet.this.remove(keys[lastIndex]);
}
}
/**
* Implements an IntIterator, used for iteration over the map's keys.
*/
private final class KeyIterator implements IntIterator {
private IntIterator iterator = new IndexIterator();
KeyIterator() { }
public boolean hasNext() {
return iterator.hasNext();
}
public int next() {
return keys[iterator.next()];
}
public void remove() {
iterator.remove();
}
}
/**
* Default capacity - in case no capacity was specified in the constructor
*/
private static int defaultCapacity = 16;
/**
* Holds the base hash entries. if the capacity is 2^N, than the base hash
* holds 2^(N+1). It can hold
*/
int[] baseHash;
/**
* The current capacity of the map. Always 2^N and never less than 16. We
* never use the zero index. It is needed to improve performance and is also
* used as "ground".
*/
private int capacity;
/**
* All objects are being allocated at map creation. Those objects are "free"
* or empty. Whenever a new pair comes along, a pair is being "allocated" or
* taken from the free-linked list. as this is just a free list.
*/
private int firstEmpty;
/**
* hashFactor is always (2^(N+1)) - 1. Used for faster hashing.
*/
private int hashFactor;
/**
* This array holds the unique keys
*/
int[] keys;
/**
* In case of collisions, we implement a double linked list of the colliding
* hash's with the following next[] and prev[]. Those are also used to store
* the "empty" list.
*/
int[] next;
private int prev;
/**
* Number of currently objects in the map.
*/
private int size;
/**
* Constructs a map with default capacity.
*/
public IntHashSet() {
this(defaultCapacity);
}
/**
* Constructs a map with given capacity. Capacity is adjusted to a native
* power of 2, with minimum of 16.
*
* @param capacity
* minimum capacity for the map.
*/
public IntHashSet(int capacity) {
this.capacity = 16;
// Minimum capacity is 16..
while (this.capacity < capacity) {
// Multiply by 2 as long as we're still under the requested capacity
this.capacity <<= 1;
}
// As mentioned, we use the first index (0) as 'Ground', so we need the
// length of the arrays to be one more than the capacity
int arrayLength = this.capacity + 1;
this.keys = new int[arrayLength];
this.next = new int[arrayLength];
// Hash entries are twice as big as the capacity.
int baseHashSize = this.capacity << 1;
this.baseHash = new int[baseHashSize];
// The has factor is 2^M - 1 which is used as an "AND" hashing operator.
// {@link #calcBaseHash()}
this.hashFactor = baseHashSize - 1;
this.size = 0;
clear();
}
/**
* Adds a pair to the map. Takes the first empty position from the
* empty-linked-list's head - {@link firstEmpty}.
*
* New pairs are always inserted to baseHash, and are followed by the old
* colliding pair.
*
* @param key
* integer which maps the given value
* @param e
* value which is being mapped using the given key
*/
private void prvt_add(int key) {
// Hash entry to which the new pair would be inserted
int hashIndex = calcBaseHashIndex(key);
// 'Allocating' a pair from the "Empty" list.
int objectIndex = firstEmpty;
// Setting data
firstEmpty = next[firstEmpty];
keys[objectIndex] = key;
// Inserting the new pair as the first node in the specific hash entry
next[objectIndex] = baseHash[hashIndex];
baseHash[hashIndex] = objectIndex;
// Announcing a new pair was added!
++size;
}
/**
* Calculating the baseHash index using the internal hashFactor
* .
*
* @param key
*/
protected int calcBaseHashIndex(int key) {
return key & hashFactor;
}
/**
* Empties the map. Generates the "Empty" space list for later allocation.
*/
public void clear() {
// Clears the hash entries
Arrays.fill(this.baseHash, 0);
// Set size to zero
size = 0;
// Mark all array entries as empty. This is done with
// firstEmpty pointing to the first valid index (1 as 0 is
// used as 'Ground').
firstEmpty = 1;
// And setting all the next[i] to point at
// i+1.
for (int i = 1; i < this.capacity;) {
next[i] = ++i;
}
// Surly, the last one should point to the 'Ground'.
next[this.capacity] = 0;
}
/**
* Checks if a given key exists in the map.
*
* @param value
* that is checked against the map data.
* @return true if the key exists in the map. false otherwise.
*/
public boolean contains(int value) {
return find(value) != 0;
}
/**
* Find the actual index of a given key.
*
* @param key
* @return index of the key. zero if the key wasn't found.
*/
protected int find(int key) {
// Calculate the hash entry.
int baseHashIndex = calcBaseHashIndex(key);
// Start from the hash entry.
int localIndex = baseHash[baseHashIndex];
// while the index does not point to the 'Ground'
while (localIndex != 0) {
// returns the index found in case of of a matching key.
if (keys[localIndex] == key) {
return localIndex;
}
// next the local index
localIndex = next[localIndex];
}
// If we got this far, it could only mean we did not find the key we
// were asked for. return 'Ground' index.
return 0;
}
/**
* Find the actual index of a given key with it's baseHashIndex.
* Some methods use the baseHashIndex. If those call {@link #find()} there's
* no need to re-calculate that hash.
*
* @param key
* @param baseHashIndex
* @return the index of the given key, or 0 as 'Ground' if the key wasn't
* found.
*/
private int findForRemove(int key, int baseHashIndex) {
// Start from the hash entry.
this.prev = 0;
int index = baseHash[baseHashIndex];
// while the index does not point to the 'Ground'
while (index != 0) {
// returns the index found in case of of a matching key.
if (keys[index] == key) {
return index;
}
// next the local index
prev = index;
index = next[index];
}
// If we got this far, it could only mean we did not find the key we
// were asked for. return 'Ground' index.
this.prev = 0;
return 0;
}
/**
* Grows the map. Allocates a new map of double the capacity, and
* fast-insert the old key-value pairs.
*/
protected void grow() {
IntHashSet that = new IntHashSet(this.capacity * 2);
// Iterates fast over the collection. Any valid pair is put into the new
// map without checking for duplicates or if there's enough space for
// it.
for (IndexIterator iterator = new IndexIterator(); iterator.hasNext();) {
int index = iterator.next();
that.prvt_add(this.keys[index]);
}
// for (int i = capacity; i > 0; --i) {
//
// that._add(this.keys[i]);
//
// }
// Copy that's data into this.
this.capacity = that.capacity;
this.size = that.size;
this.firstEmpty = that.firstEmpty;
this.keys = that.keys;
this.next = that.next;
this.baseHash = that.baseHash;
this.hashFactor = that.hashFactor;
}
/**
*
* @return true if the map is empty. false otherwise.
*/
public boolean isEmpty() {
return size == 0;
}
/**
* Returns a new iterator for the mapped objects.
*/
public IntIterator iterator() {
return new KeyIterator();
}
/**
* Prints the baseHash array, used for debug purposes.
*/
public void printBaseHash() {
for (int i = 0; i < this.baseHash.length; i++) {
if (baseHash[i] != 0) {
System.out.println(i + ".\t" + baseHash[i]);
}
}
}
/**
* Add a mapping int key -> int value.
*
* If the key was already inside just
* updating the value it refers to as the given object.
*
* Otherwise if the map is full, first {@link #grow()} the map.
*
* @param value
* integer which maps the given value
* @return true always.
*/
public boolean add(int value) {
// Does key exists?
int index = find(value);
// Yes!
if (index != 0) {
return true;
}
// Is there enough room for a new pair?
if (size == capacity) {
// No? Than grow up!
grow();
}
// Now that everything is set, the pair can be just put inside with no
// worries.
prvt_add(value);
return true;
}
/**
* Remove a pair from the map, specified by it's key.
*
* @param value
* specify the value to be removed
*
* @return true if the map was changed (the key was found and removed).
* false otherwise.
*/
public boolean remove(int value) {
int baseHashIndex = calcBaseHashIndex(value);
int index = findForRemove(value, baseHashIndex);
if (index != 0) {
// If it is the first in the collision list, we should promote its
// next colliding element.
if (prev == 0) {
baseHash[baseHashIndex] = next[index];
}
next[prev] = next[index];
next[index] = firstEmpty;
firstEmpty = index;
--size;
return true;
}
return false;
}
/**
* @return number of pairs currently in the map
*/
public int size() {
return this.size;
}
/**
* Translates the mapped pairs' values into an array of Objects
*
* @return an object array of all the values currently in the map.
*/
public int[] toArray() {
int j = -1;
int[] array = new int[size];
// Iterates over the values, adding them to the array.
for (IntIterator iterator = iterator(); iterator.hasNext();) {
array[++j] = iterator.next();
}
return array;
}
/**
* Translates the mapped pairs' values into an array of ints
*
* @param a
* the array into which the elements of the map are to be stored,
* if it is big enough; otherwise, a new array of the same
* runtime type is allocated for this purpose.
*
* @return an array containing the values stored in the map
*
*/
public int[] toArray(int[] a) {
int j = 0;
if (a.length < size) {
a = new int[size];
}
// Iterates over the values, adding them to the array.
for (IntIterator iterator = iterator(); j < a.length
&& iterator.hasNext(); ++j) {
a[j] = iterator.next();
}
return a;
}
/**
* I have no idea why would anyone call it - but for debug purposes.
* Prints the entire map, including the index, key, object, next and prev.
*/
@Override
public String toString() {
StringBuffer sb = new StringBuffer();
sb.append('{');
IntIterator iterator = iterator();
while (iterator.hasNext()) {
sb.append(iterator.next());
if (iterator.hasNext()) {
sb.append(',');
sb.append(' ');
}
}
sb.append('}');
return sb.toString();
}
public String toHashString() {
String string = "\n";
StringBuffer sb = new StringBuffer();
for (int i = 0; i < this.baseHash.length; i++) {
StringBuffer sb2 = new StringBuffer();
boolean shouldAppend = false;
sb2.append(i + ".\t");
for (int index = baseHash[i]; index != 0; index = next[index]) {
sb2.append(" -> " + keys[index] + "@" + index);
shouldAppend = true;
}
if (shouldAppend) {
sb.append(sb2);
sb.append(string);
}
}
return sb.toString();
}
}