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/* Copyright (C) 2013-2019 TU Dortmund
* This file is part of AutomataLib, http://www.automatalib.net/.
*
* Licensed 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.
*/
package net.automatalib.util.partitionrefinement;
import java.util.Iterator;
import java.util.NoSuchElementException;
/**
* A block (i.e., partition class) that is maintained during the Paige/Tarjan partition refinement algorithm (see {@link
* PaigeTarjan}).
*
* Like {@link PaigeTarjan}, this is a very low-level class that exposes a lot (almost all) of its fields directly. Care
* should be taken that instances of this class are not returned (in any form) to the API user, but are hidden behind a
* facade.
*
* @author Malte Isberner
*/
public class Block {
/**
* The index of the first element in this block in the {@link PaigeTarjan#blockData} array.
*/
public int low;
/**
* The current pointer, i.e., the delimiter between elements of this block which were found to belong to a potential
* sub-class of this block, and those that do not or have not been checked.
*
* This variable will be maintained such that either ptr == -1, or {@link #low} <= ptr <=
* {@link #high}.
*/
public int ptr = -1;
/**
* The index of the last element in this block in the {@link PaigeTarjan#blockData} array, plus one.
*/
public int high;
public Block nextBlock;
public int id;
protected Block nextInWorklist;
protected Block nextTouched;
/**
* Constructor. Creates a new block with the specified parameters.
*
* @param low
* the low index of this block's data in the {@link PaigeTarjan#blockData} array
* @param high
* the high index of this block's data in the {@link PaigeTarjan#blockData} array
* @param id
* the ID of this block
* @param next
* the next block in the block list
*/
public Block(int low, int high, int id, Block next) {
this.low = low;
this.high = high;
this.id = id;
this.nextBlock = next;
}
static Iterator blockListIterator(Block start) {
return new BlockListIterator(start);
}
/**
* Retrieves the size of this block.
*
* @return the size of this block
*/
public int size() {
return high - low;
}
/**
* Checks whether this block is empty.
*
* @return {@code true} if this block is empty, {@code false} otherwise
*/
public boolean isEmpty() {
return low >= high;
}
/**
* Splits this block, if applicable. If this block cannot be split, {@code null} is returned.
*
* A new block (the split result) is created if both {@link #ptr} > {@link #low} and {@link
* #ptr} < {@link #high}. This new block will contain either the elements between {@link #low} (inclusive)
* and {@link #ptr} (exclusive), or between {@link #ptr} (inclusive) and {@link #high} (exclusive), depending on
* whichever range is smaller. This block will be updated to contain the remaining elements.
*
* When this method returns (regardless of whether a new block is created), the {@link #ptr} field will have been
* reset to {@code -1}.
*
* @param newId
* the ID of the newly created block, if applicable
*
* @return a block
*/
public Block split(int newId) {
int ptr = this.ptr;
this.ptr = -1;
int high = this.high;
int ptrHighDiff = high - ptr;
if (ptrHighDiff == 0) {
return null;
}
int low = this.low;
Block splt;
if (ptrHighDiff > ptr - low) {
splt = new Block(low, ptr, newId, nextBlock);
this.low = ptr;
} else {
splt = new Block(ptr, high, newId, nextBlock);
this.high = ptr;
}
this.nextBlock = splt;
return splt;
}
private static final class BlockListIterator implements Iterator {
private Block curr;
BlockListIterator(Block start) {
this.curr = start;
}
@Override
public boolean hasNext() {
return curr != null;
}
@Override
public Block next() {
Block result = curr;
if (result == null) {
throw new NoSuchElementException();
}
curr = result.nextBlock;
return result;
}
}
}