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2010-05-25T14:21:17Z

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2010-05-25T10:29:58Z

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==Illustrating the generic prev_permutation algorithms==

<source lang="cpp">#include <iostream>
#include <cassert>
#include <algorithm>
#include <vector>
using namespace std;
int main()
{
vector<int> vector1(3);
for (int i = 0; i < 3; ++i)
vector1[i] = i;
// In lexicographical order the permutations of 0 1 2 are
// 0 1 2, 0 2 1, 1 0 2, 1 2 0, 2 0 1, 2 1 0.
// Show that from 0 1 2 next_permutation produces 0 2 1:
next_permutation(vector1.begin(), vector1.end());
cout << vector1[0] << " ";
cout << vector1[1] << " ";
cout << vector1[2] << " ";

cout << "\n\n\n\n\n\n";
// Show that from 0 2 1 prev_permutation() produces 0 1 2:
prev_permutation(vector1.begin(), vector1.end());
cout << vector1[0] << " ";
cout << vector1[1] << " ";
cout << vector1[2] << " ";

return 0;
}</source>
<pre class=codeResult>0 2 1

0 1 2</pre>

==Use prev_permutation to permute elements until they are sorted in descending order==

<source lang="cpp">/* The following code example is taken from the book
* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/
#include <iostream>
#include <vector>
#include <deque>
#include <list>
#include <set>
#include <map>
#include <string>
#include <algorithm>
#include <iterator>
#include <functional>
#include <numeric>
/* PRINT_ELEMENTS()
* - prints optional C-string optcstr followed by
* - all elements of the collection coll
* - separated by spaces
*/
template <class T>
inline void PRINT_ELEMENTS (const T& coll, const char* optcstr="")
{
typename T::const_iterator pos;
std::cout << optcstr;
for (pos=coll.begin(); pos!=coll.end(); ++pos) {
std::cout << *pos << " ";
}
std::cout << std::endl;
}
/* INSERT_ELEMENTS (collection, first, last)
* - fill values from first to last into the collection
* - NOTE: NO half-open range
*/
template <class T>
inline void INSERT_ELEMENTS (T& coll, int first, int last)
{
for (int i=first; i<=last; ++i) {
coll.insert(coll.end(),i);
}
}
using namespace std;
int main()
{
vector<int> coll;
INSERT_ELEMENTS(coll,1,3);
PRINT_ELEMENTS(coll,"on entry: ");
/* permute elements until they are sorted in descending order
* - runs through all permutations because the elements are sorted
* in descending order now
*/
while (prev_permutation(coll.begin(),coll.end())) {
PRINT_ELEMENTS(coll," ");
}
PRINT_ELEMENTS(coll,"afterward: ");
}</source>
<pre class=codeResult>on entry: 1 2 3
afterward: 3 2 1</pre>

==Use prev_permutation to permute until descending sorted==

<source lang="cpp">/* The following code example is taken from the book
* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/
#include <iostream>
#include <vector>
#include <deque>
#include <list>
#include <set>
#include <map>
#include <string>
#include <algorithm>
#include <iterator>
#include <functional>
#include <numeric>
/* PRINT_ELEMENTS()
* - prints optional C-string optcstr followed by
* - all elements of the collection coll
* - separated by spaces
*/
template <class T>
inline void PRINT_ELEMENTS (const T& coll, const char* optcstr="")
{
typename T::const_iterator pos;
std::cout << optcstr;
for (pos=coll.begin(); pos!=coll.end(); ++pos) {
std::cout << *pos << " ";
}
std::cout << std::endl;
}
/* INSERT_ELEMENTS (collection, first, last)
* - fill values from first to last into the collection
* - NOTE: NO half-open range
*/
template <class T>
inline void INSERT_ELEMENTS (T& coll, int first, int last)
{
for (int i=first; i<=last; ++i) {
coll.insert(coll.end(),i);
}
}
using namespace std;
int main()
{
vector<int> coll;
INSERT_ELEMENTS(coll,1,3);
PRINT_ELEMENTS(coll,"on entry: ");
/* permute until descending sorted
* - this is the next permutation after ascending sorting
* - so the loop ends immediately
*/
while (prev_permutation(coll.begin(),coll.end())) {
PRINT_ELEMENTS(coll," ");
}
PRINT_ELEMENTS(coll,"now: ");
}</source>
<pre class=codeResult>on entry: 1 2 3
now: 3 2 1</pre>

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