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/****************************************************************************
**
** Copyright (C) 2012 Digia Plc and/or its subsidiary(-ies).
** Contact: http://www.qt-project.org/legal
**
** This file is part of the Qt Mobility Components.
**
** $QT_BEGIN_LICENSE:LGPL$
** GNU Lesser General Public License Usage
** This file may be used under the terms of the GNU Lesser General Public
** License version 2.1 as published by the Free Software Foundation and
** appearing in the file LICENSE.LGPL included in the packaging of this
** file. Please review the following information to ensure the GNU Lesser
** General Public License version 2.1 requirements will be met:
** http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
**
** In addition, as a special exception, Nokia gives you certain additional
** rights. These rights are described in the Nokia Qt LGPL Exception
** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
**
** GNU General Public License Usage
** Alternatively, this file may be used under the terms of the GNU General
** Public License version 3.0 as published by the Free Software Foundation
** and appearing in the file LICENSE.GPL included in the packaging of this
** file. Please review the following information to ensure the GNU General
** Public License version 3.0 requirements will be met:
** http://www.gnu.org/copyleft/gpl.html.
**
** Other Usage
** Alternatively, this file may be used in accordance with the terms and
** conditions contained in a signed written agreement between you and Nokia.
**
**
**
**
**
**
** $QT_END_LICENSE$
**
****************************************************************************/
#ifndef QMALGORITHMS_H
#define QMALGORITHMS_H
#include "qmobilityglobal.h"
QTM_BEGIN_NAMESPACE
/*
This performs a partial sort, examining the elements in the range [start, end-1] to place the
elements of ordinality [from, to-1] in the positions [from, to-1] in order defined by lessThan.
In addition, after calling this function, elements lesser than *from will appear before "from" and
elements greater than *(to-1) will appear at or after "to".
This function runs in time O(k log k + N), where k = to-from, N = end-start. It uses an in-place
partial quicksort algorithm. See:
http://en.wikipedia.org/wiki/Selection_algorithm
Some examples using the convenience function for containers:
QList<int> list1 = ..., list2 = ...;
qPartialSort(list1, 0, 10);
QList<int> firstTen = list1.mid(0, 10);
qPartialSort(list1, 10, 20);
QList<int> secondTen = list1.mid(10, 10);
qPartialSort(list1, 20, list1.size());
QList<int> rest = list.mid(20);
// list1 is now sorted!
int mid = list2.count() / 2;
qPartialSort(list2, mid, mid+1); // O(N) time
int median = list2[mid];
*/
template<typename RandomAccessIterator, typename LessThan>
inline void qPartialSort(RandomAccessIterator start, RandomAccessIterator end,
RandomAccessIterator from, RandomAccessIterator to, LessThan lessThan)
{
// This code is based on qSort
while (true) {
if (from < start)
from = start;
if (to > end)
to = end;
int span = int(end - start);
if (span < 2 || from >= to)
return;
--end;
RandomAccessIterator low = start, high = end - 1;
RandomAccessIterator pivot = start + span / 2;
if (lessThan(*end, *start))
qSwap(*end, *start);
if (span == 2)
return;
if (lessThan(*pivot, *start))
qSwap(*pivot, *start);
if (lessThan(*end, *pivot))
qSwap(*end, *pivot);
if (span == 3)
return;
qSwap(*pivot, *end);
// Partition the elements
while (low < high) {
while (low < high && lessThan(*low, *end))
++low;
while (high > low && lessThan(*end, *high))
--high;
if (low < high) {
qSwap(*low, *high);
++low;
--high;
} else {
break;
}
}
if (lessThan(*low, *end))
pivot = low+1;
else
pivot = low;
qSwap(*end, *pivot);
++end;
// *pivot is now in the correct place in the list
if (pivot > to) {
// like qPartialSort(start, pivot, from, to, lessThan);
end = pivot;
} else if (pivot > from) { // from < pivot <= to
qSort(start, pivot, lessThan);
// like qPartialSort(pivot+1, end, pivot+1, to, lessThan);
start = pivot + 1;
from = pivot + 1;
} else { // pivot <= from < to
// like qPartialSort(pivot+1, end, from, to, lessThan);
start = pivot+1;
}
}
}
template<typename RandomAccessIterator, typename T>
inline void qPartialSortHelper(RandomAccessIterator start, RandomAccessIterator end,
RandomAccessIterator from, RandomAccessIterator to, const T& dummy)
{
Q_UNUSED(dummy);
qPartialSort(start, end, from, to, qLess<T>());
}
template<typename RandomAccessIterator>
inline void qPartialSort(RandomAccessIterator start, RandomAccessIterator end,
RandomAccessIterator from, RandomAccessIterator to)
{
qPartialSortHelper(start, end, from, to, *start);
}
template<typename Container>
inline void qPartialSort(Container& container, int from, int to)
{
qPartialSort(container.begin(), container.end(), container.begin()+from, container.begin()+to);
}
QTM_END_NAMESPACE
#endif
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