| /* |
| * |
| * 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.cassandra.utils; |
| |
| import java.util.*; |
| |
| /** |
| * A class for iterating sequentially through an ordered collection and efficiently |
| * finding the overlapping set of matching intervals. |
| * |
| * The algorithm is quite simple: the intervals are sorted ascending by both min and max |
| * in two separate lists. These lists are walked forwards each time we visit a new point, |
| * with the set of intervals in the min-ordered list being added to our set of overlaps, |
| * and those in the max-ordered list being removed. |
| */ |
| public class OverlapIterator<I extends Comparable<? super I>, V> |
| { |
| // indexing into sortedByMin, tracks the next interval to include |
| int nextToInclude; |
| final List<Interval<I, V>> sortedByMin; |
| // indexing into sortedByMax, tracks the next interval to exclude |
| int nextToExclude; |
| final List<Interval<I, V>> sortedByMax; |
| final Set<V> overlaps = new HashSet<>(); |
| final Set<V> accessible = Collections.unmodifiableSet(overlaps); |
| |
| public OverlapIterator(Collection<Interval<I, V>> intervals) |
| { |
| sortedByMax = new ArrayList<>(intervals); |
| Collections.sort(sortedByMax, Interval.<I, V>maxOrdering()); |
| // we clone after first sorting by max; this is quite likely to make sort cheaper, since a.max < b.max |
| // generally increases the likelihood that a.min < b.min, so the list may be partially sorted already. |
| // this also means if (in future) we sort either collection (or a subset thereof) by the other's comparator |
| // all items, including equal, will occur in the same order, including |
| sortedByMin = new ArrayList<>(sortedByMax); |
| Collections.sort(sortedByMin, Interval.<I, V>minOrdering()); |
| } |
| |
| // move the iterator forwards to the overlaps matching point |
| public void update(I point) |
| { |
| // we don't use binary search here since we expect points to be a superset of the min/max values |
| |
| // add those we are now after the start of |
| while (nextToInclude < sortedByMin.size() && sortedByMin.get(nextToInclude).min.compareTo(point) <= 0) |
| overlaps.add(sortedByMin.get(nextToInclude++).data); |
| // remove those we are now after the end of |
| while (nextToExclude < sortedByMax.size() && sortedByMax.get(nextToExclude).max.compareTo(point) < 0) |
| overlaps.remove(sortedByMax.get(nextToExclude++).data); |
| } |
| |
| public Set<V> overlaps() |
| { |
| return accessible; |
| } |
| } |