Q157567: STL Sample for the prev_permutation Function

Article: Q157567
Product(s): Microsoft C Compiler
Version(s): winnt:
Operating System(s): 
Keyword(s): _IK
Last Modified: 05-MAY-2001

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The information in this article applies to:

- The Standard C++ Library, included with:
   - *EDITOR Please do not choose this product*Microsoft Visual C++ 32-bit Edition* use 241, 265, 225, version 4.2 
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SUMMARY
=======

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

MORE INFORMATION
================

Required Header
---------------

     <algorithm>

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.

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.

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

REFERENCES
==========

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

Additional query words: STL reverse

======================================================================
Keywords          : _IK 
Technology        : kbVCsearch kbAudDeveloper kbVCLibrary
Version           : winnt:
Issue type        : kbhowto

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