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STL Sample for the prev_permutation Function

Retired KB ArticleThis article was written about products for which Microsoft no longer offers support. Therefore, this article is offered "as is" and will no longer be updated.
Article ID:157567
Last Review:December 2, 2003
Revision:2.0
This article was previously published under Q157567
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SUMMARY

The sample code below illustrates how to use the prev_permutation STL function in Visual C++.

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MORE INFORMATION

Required Header

   <algorithm>
				

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Prototype

   template<class BidirectionalIterator> inline
   bool prev_permutation(BidirectionalIterator first,
                         BidirectionalIterator last)
				
NOTE: The class/parameter names in the prototype do not match the version in the header file. Some have been modified to improve readability.

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Description

The prev_permutation algorithm changes the order of the elements the range [first, last), to the previous lexicographic permutation and returns true. If there is no prev_permutation it arranges the sequence to be the first permutation and returns false.

IMPORTANT: The prev_permutation algorithm assumes the sequence is sorted in descending order using operator<.

The non-predicate version uses the operator< to order the permutations.

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Sample Code

////////////////////////////////////////////////////////////////////// 
// 
// Compile options needed: /GX
// 
// prev_permutation.cpp : Illustrates how to use the prev_permutation
//                        function.
// 
// Functions:
// 
//    prev_permutation : Change the order of the sequence to the
//                       previous lexicographic permutation.
// 
// Written by Kalindi Sanghrajka
// of Microsoft Product Support Services,
// Software Core Developer Support.
// Copyright (c) 1996 Microsoft Corporation. All rights reserved.
////////////////////////////////////////////////////////////////////// 

// disable warning C4786: symbol greater than 255 character,
// okay to ignore
#pragma warning(disable: 4786)

#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <functional>
using namespace std;

void main()
{

    const int VECTOR_SIZE = 3 ;

    // Define a template class vector of strings
    typedef vector<string, allocator<string> > StrVector ;

    //Define an iterator for template class vector of strings
    typedef StrVector::iterator StrVectorIt ;

    //Define an ostream iterator for strings
    typedef ostream_iterator<string, char, char_traits<char> >
    StrOstreamIt;

    StrVector Pattern(VECTOR_SIZE) ;

    StrVectorIt start, end, it ;

    StrOstreamIt outIt(cout, " ") ;

    start = Pattern.begin() ;   // location of first
                                      // element of Pattern

    end = Pattern.end() ;       // one past the location last
                                       // element of Pattern

    //Initialize vector Pattern
    Pattern[0] = "C" ;
    Pattern[1] = "B" ;
    Pattern[2] = "A" ;

    // print content of Pattern
    cout << "Before calling prev_permutation...\n" << "Pattern: " ;
    for(it = start; it != end; it++)
        cout << *it << " " ;
    cout << "\n\n" ;

    // Generate all possible permutations

    cout << "After calling prev_permutation...." << endl ;
    while ( prev_permutation(start, end) )
    {
        copy(start, end, outIt) ;
        cout << endl ;
    }
}

Program Output is:

Before calling prev_permutation...
Pattern: C B A

After calling prev_permutation....
C A B
B C A
B A C
A C B
A B C
				

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REFERENCES

Visual C++ Books On Line: Visual C++ Books:C/C++:Standard C++ Library Reference.

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APPLIES TO
The Standard C++ Library, when used with:
  Microsoft Visual C++ 4.2 Professional Edition
  Microsoft Visual C++ 4.2 Enterprise Edition
  Microsoft Visual C++ 5.0 Learning Edition

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Keywords: 
kbcode kbhowto KB157567

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