1/*
2 * Copyright (C) 2010 The Android Open Source Project
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
17package com.replica.replicaisland;
18
19import java.util.Comparator;
20
21public class ShellSorter<Type> extends Sorter<Type> {
22/**
23 * Shell sort implementation based on the one found here:
24 * http://www.augustana.ab.ca/~mohrj/courses/2004.winter/csc310/source/ShellSort.java.html
25 * Note that the running time can be tuned by adjusting the size of the increment used
26 * to pass over the array each time.  Currently this function uses Robert Cruse's suggestion
27 * of increment = increment / 3 + 1.
28 */
29
30public void sort(Type[] array, int count, Comparator<Type> comparator) {
31    int increment = count / 3 + 1;
32
33    // Sort by insertion sort at diminishing increments.
34    while ( increment > 1 ) {
35        for ( int start = 0; start < increment; start++ ) {
36            insertionSort(array, count, start, increment, comparator);
37        }
38        increment = increment / 3 + 1;
39    }
40
41    // Do a final pass with an increment of 1.
42    // (This has to be outside the previous loop because the formula above for calculating the
43    // next increment will keep generating 1 repeatedly.)
44    insertionSort(array, count, 0, 1, comparator );
45 }
46
47
48/**
49  *  Insertion sort modified to sort elements at a
50  *  fixed increment apart.
51  *
52  *  The code can be revised to eliminate the initial
53  *  'if', but I found that it made the sort slower.
54  *
55  *  @param start      the start position
56  *  @param increment  the increment
57  */
58public void insertionSort(Type[] array, int count, int start, int increment,
59        Comparator<Type> comparator) {
60    int j;
61    int k;
62    Type temp;
63
64    for (int i = start + increment; i < count; i += increment) {
65       j = i;
66       k = j - increment;
67       int delta = comparator.compare(array[j], array[k]);
68
69       if ( delta < 0 ) {
70          // Shift all previous entries down by the current
71    	  // increment until the proper place is found.
72          temp = array[j];
73          do {
74             array[j] = array[k];
75             j = k;
76             k = j - increment;
77          } while ( j != start && comparator.compare(array[k], temp) > 0 );
78          array[j] = temp;
79       }
80    }
81  }
82}
83