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//
// QuickSort.cs
//
// Authors:
// Alejandro Serrano "Serras" (trupill@yahoo.es)
// Marek Safar <marek.safar@gmail.com>
// Jb Evain (jbevain@novell.com)
//
// (C) 2007 - 2008 Novell, Inc. (http://www.novell.com)
//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
//
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//
using System;
using System.Collections.Generic;
namespace System.Linq {
class QuickSort<TElement> {
TElement [] elements;
int [] indexes;
SortContext<TElement> context;
QuickSort (IEnumerable<TElement> source, SortContext<TElement> context)
{
this.elements = source.ToArray ();
this.indexes = CreateIndexes (elements.Length);
this.context = context;
}
static int [] CreateIndexes (int length)
{
var indexes = new int [length];
for (int i = 0; i < length; i++)
indexes [i] = i;
return indexes;
}
void PerformSort ()
{
// If the source contains just zero or one element, there's no need to sort
if (elements.Length <= 1)
return;
context.Initialize (elements);
// Then sorts the elements according to the collected
// key values and the selected ordering
Sort (0, indexes.Length - 1);
}
int CompareItems (int first_index, int second_index)
{
return context.Compare (first_index, second_index);
}
// We look at the first, middle, and last items in the subarray.
// Then we put the largest on the right side, the smallest on
// the left side, and the median becomes our pivot.
int MedianOfThree (int left, int right)
{
int center = (left + right) / 2;
if (CompareItems (indexes [center], indexes [left]) < 0)
Swap (left, center);
if (CompareItems (indexes [right], indexes [left]) < 0)
Swap (left, right);
if (CompareItems (indexes [right], indexes [center]) < 0)
Swap (center, right);
Swap (center, right - 1);
return indexes [right - 1];
}
void Sort (int left, int right)
{
if (left + 3 <= right) {
int l = left, r = right - 1, pivot = MedianOfThree (left, right);
while (true) {
while (CompareItems (indexes [++l], pivot) < 0) { }
while (CompareItems (indexes [--r], pivot) > 0) { }
if (l < r)
Swap (l, r);
else
break;
}
// Restore pivot
Swap (l, right - 1);
// Partition and sort
Sort (left, l - 1);
Sort (l + 1, right);
} else
// If there are three items in the subarray, insertion sort is better
InsertionSort (left, right);
}
void InsertionSort (int left, int right)
{
for (int i = left + 1; i <= right; i++) {
int j, tmp = indexes [i];
for (j = i; j > left && CompareItems (tmp, indexes [j - 1]) < 0; j--)
indexes [j] = indexes [j - 1];
indexes [j] = tmp;
}
}
void Swap (int left, int right)
{
int temp = indexes [right];
indexes [right] = indexes [left];
indexes [left] = temp;
}
public static IEnumerable<TElement> Sort (IEnumerable<TElement> source, SortContext<TElement> context)
{
var sorter = new QuickSort<TElement> (source, context);
sorter.PerformSort ();
for (int i = 0; i < sorter.indexes.Length; i++)
yield return sorter.elements [sorter.indexes [i]];
}
}
}
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