org.logicng.transformations.Anonymizer Maven / Gradle / Ivy
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// The Next Generation Logic Library //
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// Copyright 2015-20xx Christoph Zengler //
// //
// 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 //
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// http://www.apache.org/licenses/LICENSE-2.0 //
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// 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. //
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package org.logicng.transformations;
import static org.logicng.formulas.cache.TransformationCacheEntry.ANONYMIZATION;
import org.logicng.datastructures.Substitution;
import org.logicng.formulas.Formula;
import org.logicng.formulas.FormulaTransformation;
import org.logicng.formulas.Variable;
/**
* An anonymizer replaces all variables in a formula with new variables generated from a given prefix and a counter.
*
* An instance can be used to anonymize multiple formulas. In this case, variables with the same name will be replaced
* with the same anonymized variable.
*
* After anonymizing one or more formulas, the mapping from original variable to anonymized variable can be accessed
* via {@link #getSubstitution()}.
* @version 1.4.0
* @since 1.4.0
*/
public final class Anonymizer implements FormulaTransformation {
private final Substitution substitution;
private final String prefix;
private int counter;
/**
* Constructs a new anonymizer with a given prefix for the newly introduced variables.
* @param prefix the prefix for the new variables
* @param startCounter where should the counter start
*/
public Anonymizer(final String prefix, final int startCounter) {
this.prefix = prefix;
this.substitution = new Substitution();
this.counter = startCounter;
}
/**
* Constructs a new anonymizer with a given prefix for the newly introduced variables.
* @param prefix the prefix for the new variables
*/
public Anonymizer(final String prefix) {
this(prefix, 0);
}
/**
* Constructs a new anonymizer with the standard variable prefix 'v'.
*/
public Anonymizer() {
this("v");
}
/**
* Returns the substitution which was used to anonymize the formula(s).
*
* Although a substitution maps from variables to formulas, it is guaranteed that
* the substitution always maps to variables. So the following cast will always be
* safe:
*
* {@code (Variable) getSubstitution().getSubstitution(x)}
* @return the substitution which was used to anonymize the formula(s)
*/
public Substitution getSubstitution() {
return new Substitution(this.substitution);
}
@Override
public Formula apply(final Formula formula, final boolean cache) {
if (formula.variables().isEmpty()) {
return formula;
}
final Formula cached = formula.transformationCacheEntry(ANONYMIZATION);
if (cache && cached != null) {
return cached;
}
for (final Variable variable : formula.variables()) {
if (this.substitution.getSubstitution(variable) == null) {
this.substitution.addMapping(variable, formula.factory().variable(this.prefix + this.counter++));
}
}
final Formula transformed = formula.substitute(this.substitution);
if (cache) {
formula.setTransformationCacheEntry(ANONYMIZATION, transformed);
}
return transformed;
}
}