/*
* Copyright (c) 2013-2017 Cinchapi 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 com.cinchapi.concourse.util;
import java.util.Comparator;
import java.util.Iterator;
import java.util.Set;
import java.util.SortedSet;
import com.google.common.collect.Sets;
/**
* Utilities for {@link Set} objects. This class is mostly designed to offer
* performance improvements over some of the operations in the Guava
* {@link Sets} class.
*
* @author Jeff Nelson
*/
public class TSets {
/**
* Return a Set that contains only the elements that are in both {@code a}
* and {@code b}.
*
* @param a
* @param b
* @return the intersection of the Sets
*/
public static <T> Set<T> intersection(Set<T> a, Set<T> b) {
if(a instanceof SortedSet && b instanceof SortedSet) {
return sortedIntersection((SortedSet<T>) a, (SortedSet<T>) b);
}
else {
Set<T> intersection = Sets.newLinkedHashSet();
Set<T> smaller = a.size() <= b.size() ? a : b;
Set<T> larger = Sets.newHashSet(a.size() > b.size() ? a : b);
for (T element : smaller) {
if(larger.contains(element)) {
intersection.add(element);
}
}
return intersection;
}
}
/**
* Return a Set that contains all the elements in both {@code a} and
* {@code b}.
*
* @param a
* @param b
* @return the union of the Sets
*/
public static <T> Set<T> union(Set<T> a, Set<T> b) {
Set<T> union = Sets.newLinkedHashSet(a);
union.addAll(b);
return union;
}
/**
* Perform an optimized intersection calculation, assuming that both
* {@code a} and {@code b} are sorted sets.
*
* @param a
* @param b
* @return the intersection of the Sets
*/
@SuppressWarnings("unchecked")
private static <T> Set<T> sortedIntersection(SortedSet<T> a, SortedSet<T> b) {
Set<T> intersection = Sets.newLinkedHashSet();
if(a.isEmpty() || b.isEmpty()) {
return intersection;
}
Iterator<T> ait = a.iterator();
Iterator<T> bit = b.iterator();
Comparator<? super T> comp = a.comparator();
boolean ago = true;
boolean bgo = true;
T aelt = null;
T belt = null;
while (((ago && ait.hasNext()) || !ago)
&& ((bgo && bit.hasNext()) || !bgo)) {
aelt = ago ? ait.next() : aelt;
belt = bgo ? bit.next() : belt;
int order = comp == null ? ((Comparable<T>) aelt).compareTo(belt)
: comp.compare(aelt, belt);
if(order == 0) {
intersection.add(aelt);
ago = true;
bgo = true;
}
else if(order > 0) {
bgo = true;
ago = false;
}
else {
ago = true;
bgo = false;
}
}
return intersection;
}
}