Microsoft KB Archive/157567

= STL Sample for the prev_permutation Function =

Article ID: 157567

Article Last Modified on 12/2/2003

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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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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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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
 * 1) pragma warning(disable: 4786)

using namespace std;
 * 1) include
 * 2) include
 * 3) include
 * 4) include
 * 5) include

void main {

const int VECTOR_SIZE = 3 ;

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