| /* |
| * Licensed to the Apache Software Foundation (ASF) under one or more |
| * contributor license agreements. See the NOTICE file distributed with |
| * this work for additional information regarding copyright ownership. |
| * The ASF licenses this file to You 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.apache.lucene.util; |
| |
| |
| import java.util.Iterator; |
| import java.util.NoSuchElementException; |
| |
| /** |
| * Provides a merged sorted view from several sorted iterators. |
| * <p> |
| * If built with <code>removeDuplicates</code> set to true and an element |
| * appears in multiple iterators then it is deduplicated, that is this iterator |
| * returns the sorted union of elements. |
| * <p> |
| * If built with <code>removeDuplicates</code> set to false then all elements |
| * in all iterators are returned. |
| * <p> |
| * Caveats: |
| * <ul> |
| * <li>The behavior is undefined if the iterators are not actually sorted. |
| * <li>Null elements are unsupported. |
| * <li>If removeDuplicates is set to true and if a single iterator contains |
| * duplicates then they will not be deduplicated. |
| * <li>When elements are deduplicated it is not defined which one is returned. |
| * <li>If removeDuplicates is set to false then the order in which duplicates |
| * are returned isn't defined. |
| * </ul> |
| * @lucene.internal |
| */ |
| public final class MergedIterator<T extends Comparable<T>> implements Iterator<T> { |
| private T current; |
| private final TermMergeQueue<T> queue; |
| private final SubIterator<T>[] top; |
| private final boolean removeDuplicates; |
| private int numTop; |
| |
| @SuppressWarnings({"unchecked","rawtypes"}) |
| public MergedIterator(Iterator<T>... iterators) { |
| this(true, iterators); |
| } |
| |
| @SuppressWarnings({"unchecked","rawtypes"}) |
| public MergedIterator(boolean removeDuplicates, Iterator<T>... iterators) { |
| this.removeDuplicates = removeDuplicates; |
| queue = new TermMergeQueue<>(iterators.length); |
| top = new SubIterator[iterators.length]; |
| int index = 0; |
| for (Iterator<T> iterator : iterators) { |
| if (iterator.hasNext()) { |
| SubIterator<T> sub = new SubIterator<>(); |
| sub.current = iterator.next(); |
| sub.iterator = iterator; |
| sub.index = index++; |
| queue.add(sub); |
| } |
| } |
| } |
| |
| @Override |
| public boolean hasNext() { |
| if (queue.size() > 0) { |
| return true; |
| } |
| |
| for (int i = 0; i < numTop; i++) { |
| if (top[i].iterator.hasNext()) { |
| return true; |
| } |
| } |
| return false; |
| } |
| |
| @Override |
| public T next() { |
| // restore queue |
| pushTop(); |
| |
| // gather equal top elements |
| if (queue.size() > 0) { |
| pullTop(); |
| } else { |
| current = null; |
| } |
| if (current == null) { |
| throw new NoSuchElementException(); |
| } |
| return current; |
| } |
| |
| @Override |
| public void remove() { |
| throw new UnsupportedOperationException(); |
| } |
| |
| private void pullTop() { |
| assert numTop == 0; |
| top[numTop++] = queue.pop(); |
| if (removeDuplicates) { |
| // extract all subs from the queue that have the same top element |
| while (queue.size() != 0 |
| && queue.top().current.equals(top[0].current)) { |
| top[numTop++] = queue.pop(); |
| } |
| } |
| current = top[0].current; |
| } |
| |
| private void pushTop() { |
| // call next() on each top, and put back into queue |
| for (int i = 0; i < numTop; i++) { |
| if (top[i].iterator.hasNext()) { |
| top[i].current = top[i].iterator.next(); |
| queue.add(top[i]); |
| } else { |
| // no more elements |
| top[i].current = null; |
| } |
| } |
| numTop = 0; |
| } |
| |
| private static class SubIterator<I extends Comparable<I>> { |
| Iterator<I> iterator; |
| I current; |
| int index; |
| } |
| |
| private static class TermMergeQueue<C extends Comparable<C>> extends PriorityQueue<SubIterator<C>> { |
| TermMergeQueue(int size) { |
| super(size); |
| } |
| |
| @Override |
| protected boolean lessThan(SubIterator<C> a, SubIterator<C> b) { |
| final int cmp = a.current.compareTo(b.current); |
| if (cmp != 0) { |
| return cmp < 0; |
| } else { |
| return a.index < b.index; |
| } |
| } |
| } |
| } |