org.apache.hadoop.util.HeapSort Maven / Gradle / Ivy
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* 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.hadoop.util;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
/**
* An implementation of the core algorithm of HeapSort.
*/
@InterfaceAudience.Private
@InterfaceStability.Unstable
public final class HeapSort implements IndexedSorter {
public HeapSort() { }
private static void downHeap(final IndexedSortable s, final int b,
int i, final int N) {
for (int idx = i << 1; idx < N; idx = i << 1) {
if (idx + 1 < N && s.compare(b + idx, b + idx + 1) < 0) {
if (s.compare(b + i, b + idx + 1) < 0) {
s.swap(b + i, b + idx + 1);
} else return;
i = idx + 1;
} else if (s.compare(b + i, b + idx) < 0) {
s.swap(b + i, b + idx);
i = idx;
} else return;
}
}
/**
* Sort the given range of items using heap sort.
* {@inheritDoc}
*/
@Override
public void sort(IndexedSortable s, int p, int r) {
sort(s, p, r, null);
}
@Override
public void sort(final IndexedSortable s, final int p, final int r,
final Progressable rep) {
final int N = r - p;
// build heap w/ reverse comparator, then write in-place from end
final int t = Integer.highestOneBit(N);
for (int i = t; i > 1; i >>>= 1) {
for (int j = i >>> 1; j < i; ++j) {
downHeap(s, p-1, j, N + 1);
}
if (null != rep) {
rep.progress();
}
}
for (int i = r - 1; i > p; --i) {
s.swap(p, i);
downHeap(s, p - 1, 1, i - p + 1);
}
}
}