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Copy pathIxOrderedMergeArray.java
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142 lines (119 loc) · 3.94 KB
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/*
* Copyright 2011-2016 David Karnok
*
* 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 ix;
import java.util.*;
/**
* Merges an array of Iterable items by picking the smallest from them
* with the help of a Comparator.
*
* @param <T> the value type
*/
final class IxOrderedMergeArray<T> extends Ix<T> {
final Iterable<? extends T>[] sources;
final Comparator<? super T> comparator;
IxOrderedMergeArray(Iterable<? extends T>[] sources, Comparator<? super T> comparator) {
this.sources = sources;
this.comparator = comparator;
}
@Override
public Iterator<T> iterator() {
Iterable<? extends T>[] all = sources;
int n = all.length;
@SuppressWarnings("unchecked")
Iterator<? extends T>[] srcs = new Iterator[n];
for (int i = 0; i < n; i++) {
srcs[i] = all[i].iterator();
}
return new OrderedMergeIterator<T>(srcs, n, comparator);
}
static final class OrderedMergeIterator<T> implements Iterator<T> {
final Iterator<? extends T>[] sources;
final Comparator<? super T> comparator;
final int n;
final Object[] latest;
static final Object EMPTY = new Object();
static final Object DONE = new Object();
boolean done;
int index;
OrderedMergeIterator(Iterator<? extends T>[] sources, int n, Comparator<? super T> comparator) {
this.sources = sources;
this.n = n;
this.latest = new Object[n];
Arrays.fill(latest, EMPTY);
this.comparator = comparator;
this.index = -1;
}
@SuppressWarnings("unchecked")
@Override
public boolean hasNext() {
int i = index;
if (i < 0) {
if (done) {
return false;
}
int count = n;
Object[] vs = latest;
int d = 0;
int f = -1;
T min = null;
for (int j = 0; j < count; j++) {
Object o = vs[j];
if (o == DONE) {
d++;
continue;
} else
if (o == EMPTY) {
Iterator<? extends T> src = sources[j];
if (src.hasNext()) {
o = src.next();
vs[j] = o;
} else {
d++;
vs[j] = DONE;
continue;
}
}
if (f < 0 || comparator.compare(min, (T)o) > 0) {
f = j;
min = (T)o;
}
}
if (d == count) {
done = true;
return false;
}
index = f;
}
return true;
}
@Override
public T next() {
if (hasNext()) {
int i = index;
index = -1;
@SuppressWarnings("unchecked")
T v = (T)latest[i];
latest[i] = EMPTY;
return v;
}
throw new NoSuchElementException();
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
}
}