/*
* dk.brics.automaton
*
* Copyright (c) 2001-2009 Anders Moeller
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. The name of the author may not be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
package org.apache.lucene.util.automaton;
import java.util.ArrayList;
import java.util.LinkedList;
/**
* Operations for minimizing automata.
*
* @lucene.experimental
*/
final public class MinimizationOperations {
private MinimizationOperations() {}
/**
* Minimizes (and determinizes if not already deterministic) the given
* automaton.
*
* @see Automaton#setMinimization(int)
*/
public static void minimize(Automaton a) {
if (!a.isSingleton()) {
minimizeHopcroft(a);
}
// recompute hash code
//a.hash_code = 1a.getNumberOfStates() * 3 + a.getNumberOfTransitions() * 2;
//if (a.hash_code == 0) a.hash_code = 1;
}
private static <T> void initialize(ArrayList<T> list, int size) {
for (int i = 0; i < size; i++)
list.add(null);
}
/**
* Minimizes the given automaton using Hopcroft's algorithm.
*/
public static void minimizeHopcroft(Automaton a) {
a.determinize();
if (a.initial.numTransitions == 1) {
Transition t = a.initial.transitionsArray[0];
if (t.to == a.initial && t.min == Character.MIN_CODE_POINT
&& t.max == Character.MAX_CODE_POINT) return;
}
a.totalize();
int[] sigma = a.getStartPoints();
// initialize data structures
ArrayList<ArrayList<LinkedList<State>>> reverse = new ArrayList<ArrayList<LinkedList<State>>>();
final State[] states = a.getNumberedStates();
for (int q = 0; q < states.length; q++) {
ArrayList<LinkedList<State>> v = new ArrayList<LinkedList<State>>();
initialize(v, sigma.length);
reverse.add(v);
}
boolean[][] reverse_nonempty = new boolean[states.length][sigma.length];
ArrayList<LinkedList<State>> partition = new ArrayList<LinkedList<State>>();
initialize(partition, states.length);
int[] block = new int[states.length];
StateList[][] active = new StateList[states.length][sigma.length];
StateListNode[][] active2 = new StateListNode[states.length][sigma.length];
LinkedList<IntPair> pending = new LinkedList<IntPair>();
boolean[][] pending2 = new boolean[sigma.length][states.length];
ArrayList<State> split = new ArrayList<State>();
boolean[] split2 = new boolean[states.length];
ArrayList<Integer> refine = new ArrayList<Integer>();
boolean[] refine2 = new boolean[states.length];
ArrayList<ArrayList<State>> splitblock = new ArrayList<ArrayList<State>>();
initialize(splitblock, states.length);
for (int q = 0; q < states.length; q++) {
splitblock.set(q, new ArrayList<State>());
partition.set(q, new LinkedList<State>());
for (int x = 0; x < sigma.length; x++) {
reverse.get(q).set(x, new LinkedList<State>());
active[q][x] = new StateList();
}
}
// find initial partition and reverse edges
for (int q = 0; q < states.length; q++) {
State qq = states[q];
int j;
if (qq.accept) j = 0;
else j = 1;
partition.get(j).add(qq);
block[qq.number] = j;
for (int x = 0; x < sigma.length; x++) {
int y = sigma[x];
State p = qq.step(y);
reverse.get(p.number).get(x).add(qq);
reverse_nonempty[p.number][x] = true;
}
}
// initialize active sets
for (int j = 0; j <= 1; j++)
for (int x = 0; x < sigma.length; x++)
for (State qq : partition.get(j))
if (reverse_nonempty[qq.number][x]) active2[qq.number][x] = active[j][x]
.add(qq);
// initialize pending
for (int x = 0; x < sigma.length; x++) {
int a0 = active[0][x].size;
int a1 = active[1][x].size;
int j;
if (a0 <= a1) j = 0;
else j = 1;
pending.add(new IntPair(j, x));
pending2[x][j] = true;
}
// process pending until fixed point
int k = 2;
while (!pending.isEmpty()) {
IntPair ip = pending.removeFirst();
int p = ip.n1;
int x = ip.n2;
pending2[x][p] = false;
// find states that need to be split off their blocks
for (StateListNode m = active[p][x].first; m != null; m = m.next)
for (State s : reverse.get(m.q.number).get(x))
if (!split2[s.number]) {
split2[s.number] = true;
split.add(s);
int j = block[s.number];
splitblock.get(j).add(s);
if (!refine2[j]) {
refine2[j] = true;
refine.add(j);
}
}
// refine blocks
for (int j : refine) {
if (splitblock.get(j).size() < partition.get(j).size()) {
LinkedList<State> b1 = partition.get(j);
LinkedList<State> b2 = partition.get(k);
for (State s : splitblock.get(j)) {
b1.remove(s);
b2.add(s);
block[s.number] = k;
for (int c = 0; c < sigma.length; c++) {
StateListNode sn = active2[s.number][c];
if (sn != null && sn.sl == active[j][c]) {
sn.remove();
active2[s.number][c] = active[k][c].add(s);
}
}
}
// update pending
for (int c = 0; c < sigma.length; c++) {
int aj = active[j][c].size;
int ak = active[k][c].size;
if (!pending2[c][j] && 0 < aj && aj <= ak) {
pending2[c][j] = true;
pending.add(new IntPair(j, c));
} else {
pending2[c][k] = true;
pending.add(new IntPair(k, c));
}
}
k++;
}
for (State s : splitblock.get(j))
split2[s.number] = false;
refine2[j] = false;
splitblock.get(j).clear();
}
split.clear();
refine.clear();
}
// make a new state for each equivalence class, set initial state
State[] newstates = new State[k];
for (int n = 0; n < newstates.length; n++) {
State s = new State();
newstates[n] = s;
for (State q : partition.get(n)) {
if (q == a.initial) a.initial = s;
s.accept = q.accept;
s.number = q.number; // select representative
q.number = n;
}
}
// build transitions and set acceptance
for (int n = 0; n < newstates.length; n++) {
State s = newstates[n];
s.accept = states[s.number].accept;
for (Transition t : states[s.number].getTransitions())
s.addTransition(new Transition(t.min, t.max, newstates[t.to.number]));
}
a.clearNumberedStates();
a.removeDeadTransitions();
}
static class IntPair {
int n1, n2;
IntPair(int n1, int n2) {
this.n1 = n1;
this.n2 = n2;
}
}
static class StateList {
int size;
StateListNode first, last;
StateListNode add(State q) {
return new StateListNode(q, this);
}
}
static class StateListNode {
State q;
StateListNode next, prev;
StateList sl;
StateListNode(State q, StateList sl) {
this.q = q;
this.sl = sl;
if (sl.size++ == 0) sl.first = sl.last = this;
else {
sl.last.next = this;
prev = sl.last;
sl.last = this;
}
}
void remove() {
sl.size--;
if (sl.first == this) sl.first = next;
else prev.next = next;
if (sl.last == this) sl.last = prev;
else next.prev = prev;
}
}
}