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/*******************************************************************************
* Copyright (c) 2010-2018, Gabor Bergmann, IncQuery Labs Ltd.
* This program and the accompanying materials are made available under the
* terms of the Eclipse Public License v. 2.0 which is available at
* http://www.eclipse.org/legal/epl-v20.html.
*
* SPDX-License-Identifier: EPL-2.0
*******************************************************************************/
package tools.refinery.viatra.runtime.matchers.algorithms;
import java.util.Comparator;
import java.util.Iterator;
import java.util.NoSuchElementException;
/**
* @author Gabor Bergmann
* @since 2.1
*
*/
public class OrderedIterableMerge {
private OrderedIterableMerge() {
// Hidden utility class constructor
}
/**
* Lazily merges two iterables, each ordered according to a given comparator.
* Retains order in the result, and also eliminates any duplicates that appear in both arguments.
*/
public static <T> Iterable<T> mergeUniques(Iterable<T> first, Iterable<T> second, Comparator<T> comparator) {
return () -> new Iterator<T>() {
Iterator<T> firstIterator = first.iterator();
Iterator<T> secondIterator = second.iterator();
T firstItem;
T secondItem;
{
fetchFirst();
fetchSecond();
}
private T fetchFirst() {
T previous = firstItem;
if (firstIterator.hasNext())
firstItem = firstIterator.next();
else
firstItem = null;
return previous;
}
private T fetchSecond() {
T previous = secondItem;
if (secondIterator.hasNext())
secondItem = secondIterator.next();
else
secondItem = null;
return previous;
}
@Override
public boolean hasNext() {
return firstItem != null || secondItem != null;
}
@Override
public T next() {
if (!hasNext()) throw new NoSuchElementException();
if (firstItem != null && secondItem != null) {
if (secondItem == firstItem) { // duplicates
fetchFirst();
return fetchSecond();
} else if (comparator.compare(firstItem, secondItem) < 0) {
return fetchFirst();
} else {
return fetchSecond();
}
} else if (firstItem != null) {
return fetchFirst();
} else { // secondItem must be non-null
return fetchSecond();
}
}
};
}
}
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