/*
* Copyright 2014 JBoss Inc
*
* 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 org.optaplanner.examples.nqueens.solver.solution;
import java.util.List;
import org.optaplanner.core.impl.phase.custom.CustomPhaseCommand;
import org.optaplanner.core.impl.score.director.ScoreDirector;
import org.optaplanner.examples.nqueens.domain.NQueens;
import org.optaplanner.examples.nqueens.domain.Queen;
import org.optaplanner.examples.nqueens.domain.Row;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* Because N Queens is not NP-complete or NP-hard, it can be cheated.
* For this reason, N queens should not be used for benchmarking purposes.
* <p/>
* This class solves any N Queens instance using a polynomial time algorithm
* (<a href="http://en.wikipedia.org/wiki/Eight_queens_puzzle#Explicit_solutions">>explicit solutions algorithm</a>).
*/
public class CheatingNQueensPhaseCommand implements CustomPhaseCommand {
protected final transient Logger logger = LoggerFactory.getLogger(getClass());
public void changeWorkingSolution(ScoreDirector scoreDirector) {
NQueens nQueens = (NQueens) scoreDirector.getWorkingSolution();
int n = nQueens.getN();
List<Queen> queenList = nQueens.getQueenList();
List<Row> rowList = nQueens.getRowList();
if (n % 2 == 1) {
Queen a = queenList.get(n - 1);
scoreDirector.beforeVariableChanged(a, "row");
a.setRow(rowList.get(n - 1));
scoreDirector.afterVariableChanged(a, "row");
n--;
}
int halfN = n / 2;
if (n % 6 != 2) {
for (int i = 0; i < halfN; i++) {
Queen a = queenList.get(i);
scoreDirector.beforeVariableChanged(a, "row");
a.setRow(rowList.get((2 * i) + 1));
scoreDirector.afterVariableChanged(a, "row");
Queen b = queenList.get(halfN + i);
scoreDirector.beforeVariableChanged(b, "row");
b.setRow(rowList.get(2 * i));
scoreDirector.afterVariableChanged(b, "row");
}
} else {
for (int i = 0; i < halfN; i++) {
Queen a = queenList.get(i);
scoreDirector.beforeVariableChanged(a, "row");
a.setRow(rowList.get((halfN + (2 * i) - 1) % n));
scoreDirector.afterVariableChanged(a, "row");
Queen b = queenList.get(n - i - 1);
scoreDirector.beforeVariableChanged(b, "row");
b.setRow(rowList.get(n - 1 - ((halfN + (2 * i) - 1) % n)));
scoreDirector.afterVariableChanged(b, "row");
}
}
}
}