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1   /*
2    * Copyright 2024 Hochschule Luzern Informatik.
3    *
4    * Licensed under the Apache License, Version 2.0 (the "License");
5    * you may not use this file except in compliance with the License.
6    * You may obtain a copy of the License at
7    *
8    *      http://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS,
12   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13   * See the License for the specific language governing permissions and
14   * limitations under the License.
15   */
16  package ch.hslu.exercises.sw11.ex1.n41.array.sort;
17  
18  import java.util.Arrays;
19  import java.util.concurrent.RecursiveAction;
20  
21  /**
22   * Codebeispiel zu RecursiveAction für die Sortierung eines int-Arrays.
23   */
24  public final class SortTask extends RecursiveAction {
25  
26      private static final int THRESHOLD = 5;
27      private final int[] array;
28      private final int min;
29      private final int max;
30  
31      /**
32       * Erzeugt einen Array-Sortier Task.
33       *
34       * @param array Interger-Array.
35       */
36      public SortTask(final int[] array) {
37          this(array, 0, array.length);
38      }
39  
40      private SortTask(final int[] array, final int min, final int max) {
41          this.array = array;
42          this.min = min;
43          this.max = max;
44      }
45  
46      @Override
47      protected void compute() {
48          if (max - min < THRESHOLD) {
49              sortSequentially(min, max);
50          } else {
51              final int mid = min + (max - min) / 2;
52              invokeAll(new SortTask(array, min, mid), new SortTask(array, mid, max));
53              merge(min, mid, max);
54          }
55      }
56  
57      private void sortSequentially(final int min, final int max) {
58          //Arrays.sort(array, min, max);
59          //Arrays.parallelSort(array, min, max);
60          InsertionSort.exec(array, min, max);
61      }
62  
63      private void merge(final int min, final int mid, final int max) {
64          // vordere Hälfte von array in Hilfsarray buf kopieren
65          int[] buf = Arrays.copyOfRange(array, min, mid);
66          int i = 0;
67          int j = min;
68          int k = mid;
69          while (i < buf.length) {
70              // jeweils das nächstgrösste Element zurückkopieren
71              // bei k == max, Rest von buf zurückkopieren, falls vorhanden
72              if (k == max || buf[i] < array[k]) {
73                  array[j] = buf[i];
74                  i++;
75              } else {
76                  array[j] = array[k];
77                  k++;
78              }
79              j++;
80          }
81      }
82  }