mcs/class/System.Core/System.Linq/InternalOrderedSequence.cs

   1 //
   2 // InternalOrderedSequence.cs
   3 //
   4 // Authors:
   5 //      Alejandro Serrano "Serras" (trupill@yahoo.es)
   6 //      Marek Safar  <marek.safar@gmail.com>
   7 //
   8 // Copyright (C) 2007 Novell, Inc (http://www.novell.com)
   9 //
  10 // Permission is hereby granted, free of charge, to any person obtaining
  11 // a copy of this software and associated documentation files (the
  12 // "Software"), to deal in the Software without restriction, including
  13 // without limitation the rights to use, copy, modify, merge, publish,
  14 // distribute, sublicense, and/or sell copies of the Software, and to
  15 // permit persons to whom the Software is furnished to do so, subject to
  16 // the following conditions:
  17 //
  18 // The above copyright notice and this permission notice shall be
  19 // included in all copies or substantial portions of the Software.
  20 //
  21 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  22 // EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  23 // MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  24 // NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
  25 // LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
  26 // OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
  27 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  28 //
  29
  30 using System;
  31 using System.Collections;
  32 using System.Collections.Generic;
  33
  34 namespace System.Linq
  35 {
  36         sealed class InternalOrderedSequence<TElement, TKey> : AOrderedEnumerable<TElement>
  37         {
  38                 readonly IEnumerable<TElement> source;
  39                 readonly Func<TElement, TKey> key_selector;
  40                 readonly IComparer<TKey> comparer;
  41                 readonly bool descending;
  42
  43                 internal InternalOrderedSequence (IEnumerable<TElement> source, Func<TElement, TKey> keySelector,
  44                                                   IComparer<TKey> comparer, bool descending)
  45                 {
  46                         this.source = source;
  47                         this.key_selector = keySelector;
  48                         this.comparer = comparer ?? Comparer<TKey>.Default;
  49                         this.descending = descending;
  50                 }
  51
  52                 public override IEnumerable<TElement> Sort (IEnumerable<TElement> parentSource)
  53                 {
  54                         if (parent != null)
  55                                 return parent.Sort (source);
  56                         return PerformSort (parentSource);
  57                 }
  58
  59                 public override IEnumerator<TElement> GetEnumerator ()
  60                 {
  61                         return PerformSort (source).GetEnumerator ();
  62                 }
  63
  64                 List<TElement> source_list;
  65                 TKey[] keys;
  66                 int[] indexes;
  67
  68                 IEnumerable<TElement> PerformSort (IEnumerable<TElement> items)
  69                 {
  70                         // It first enumerates source, collecting all elements
  71                         source_list = new List<TElement> (items);
  72
  73                         // If the source contains just zero or one element, there's no need to sort
  74                         if (source_list.Count <= 1)
  75                                 return source_list;
  76
  77                         // Then evaluate the keySelector function for each element,
  78                         // collecting the key values
  79                         keys = new TKey [source_list.Count];
  80                         indexes = new int [source_list.Count];
  81                         for (int i = 0; i < source_list.Count; i++) {
  82                                 keys [i] = key_selector (source_list [i]);
  83                                 indexes [i] = i;
  84                         }
  85
  86                         // Then sorts the elements according to the collected
  87                         // key values and the selected ordering
  88                         QuickSort(0, indexes.Length - 1);
  89
  90                         // Return the values as IEnumerable<TElement>
  91                         TElement[] orderedList = new TElement [indexes.Length];
  92                         for (int i = 0; i < indexes.Length; i++)
  93                                 orderedList [i] = source_list [indexes [i]];
  94                         return orderedList;
  95                 }
  96
  97                 int CompareItems (int firstIndex, int secondIndex)
  98                 {
  99                         int comparison = comparer.Compare (keys [firstIndex], keys [secondIndex]);
 100
 101                         // If descending, return the opposite comparison
 102                         return (descending ? -comparison : comparison);
 103                 }
 104
 105                 // We look at the first, middle, and last items in the subarray.
 106                 // Then we put the largest on the right side, the smallest on
 107                 // the left side, and the median becomes our pivot.
 108                 int MedianOfThree (int left, int right)
 109                 {
 110                         int center = (left + right) / 2;
 111                         if (CompareItems (indexes [center], indexes [left]) < 0)
 112                                 Swap (left, center);
 113                         if (CompareItems (indexes [right], indexes [left]) < 0)
 114                                 Swap (left, right);
 115                         if (CompareItems (indexes [right], indexes [center]) < 0)
 116                                 Swap (center, right);
 117                         Swap (center, right - 1);
 118                         return indexes [right - 1];
 119                 }
 120
 121                 void QuickSort (int left, int right)
 122                 {
 123                         if (left + 3 <= right) {
 124                                 int l = left, r = right - 1, pivot = MedianOfThree (left, right);
 125                                 while (true) {
 126                                         while (CompareItems (indexes [++l], pivot) < 0) {}
 127                                         while (CompareItems (indexes [--r], pivot) > 0) {}
 128                                         if (l < r)
 129                                                 Swap (l, r);
 130                                         else
 131                                                 break;
 132                                 }
 133                                 // Restore pivot
 134                                 Swap (l, right - 1);
 135                                 // Partition and sort
 136                                 QuickSort (left, l - 1);
 137                                 QuickSort (l + 1, right);
 138                         } else
 139                                 // If there are three items in the subarray, insertion sort is better
 140                                 InsertionSort (left, right);
 141                 }
 142
 143                 void InsertionSort (int left, int right)
 144                 {
 145                         for (int i = left + 1; i <= right; i++) {
 146                                 int j, tmp = indexes [i];
 147                                 for (j = i; j > left && CompareItems (tmp, indexes [j - 1]) < 0; j--)
 148                                      indexes [j] = indexes [j - 1];
 149                                 indexes [j] = tmp;
 150                         }
 151                 }
 152
 153                 void Swap (int left, int right)
 154                 {
 155                         int temp = indexes [right];
 156                         indexes [right] = indexes [left];
 157                         indexes [left] = temp;
 158                 }
 159
 160         }
 161 }