| /* |
| * 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.wayang.core.util; |
| |
| import java.util.ArrayList; |
| import java.util.List; |
| |
| /** |
| * Iterates all combinations, i.e., the Cartesian product, of given {@link Iterable}s. |
| */ |
| public class CrossProductIterable<T> implements Iterable<List<T>> { |
| |
| public final List<? extends Iterable<T>> iterables; |
| |
| public CrossProductIterable(List<? extends Iterable<T>> iterables) { |
| this.iterables = new ArrayList<>(iterables); |
| } |
| |
| @Override |
| public java.util.Iterator<List<T>> iterator() { |
| return new CrossProductIterable.Iterator<>(this); |
| } |
| |
| private static class Iterator<T> implements java.util.Iterator<List<T>> { |
| |
| private final CrossProductIterable<T> crossProductIterable; |
| |
| private final List<java.util.Iterator<T>> partialIterators; |
| |
| private List<T> vals; |
| |
| private boolean hasEmptyIterator; |
| |
| |
| private Iterator(CrossProductIterable<T> crossProductIterable) { |
| // Initialize. |
| this.crossProductIterable = crossProductIterable; |
| this.partialIterators = new ArrayList<>(this.crossProductIterable.iterables.size()); |
| this.vals = new ArrayList<>(this.crossProductIterable.iterables.size()); |
| |
| for (Iterable<T> iterable : this.crossProductIterable.iterables) { |
| final java.util.Iterator<T> iterator = iterable.iterator(); |
| this.partialIterators.add(iterator); |
| this.hasEmptyIterator |= !iterator.hasNext(); |
| this.vals.add(null); |
| } |
| |
| } |
| |
| @Override |
| public boolean hasNext() { |
| if (this.hasEmptyIterator) return false; |
| for (java.util.Iterator<T> partialIterator : this.partialIterators) { |
| if (partialIterator.hasNext()) return true; |
| } |
| return false; |
| } |
| |
| @Override |
| public List<T> next() { |
| assert this.hasNext(); |
| |
| List<T> next = new ArrayList<>(this.partialIterators.size()); |
| boolean isFetchNext = true; |
| for (int i = 0; i < this.partialIterators.size(); i++) { |
| java.util.Iterator<T> partialIterator = this.partialIterators.get(i); |
| if (isFetchNext) { |
| // If the Iterator has made a full pass, replace it with a new one. |
| boolean isFullPass; |
| if (isFullPass = !partialIterator.hasNext()) { |
| assert i < this.partialIterators.size() - 1; |
| partialIterator = this.crossProductIterable.iterables.get(i).iterator(); |
| this.partialIterators.set(i, partialIterator); |
| assert partialIterator.hasNext(); |
| } |
| |
| // If the Iterator had made a full pass or this is the very first iteration. |
| if (isFetchNext) { |
| isFetchNext = isFullPass || this.vals.get(i) == null; |
| this.vals.set(i, partialIterator.next()); |
| } |
| } |
| |
| next.add(this.vals.get(i)); |
| } |
| |
| return next; |
| } |
| } |
| } |