Predicate Version of next_permutation (STL Sample)

The sample code below illustrates how to use the predicate version of the next_permutation STL function in Visual C++.

Required Header:
<algorithm>

template<class BidirectionalIterator, class Compare> inline
     bool next_permutation(BidirectionalIterator first,
     BidirectionalIterator last,
     Compare compare)

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 next_permutation algorithm changes the order of the elements in the range [first, last) to the next lexicographic permutation and returns true. If there is no next_permutation, it arranges the sequence to be the first permutation and returns false. NOTE: The next_permutation algorithm assumes that the sequence is sorted in ascending order using the compare function. The non-predicate version uses the compare function to order the permutations.

Sample Code:

//////////////////////////////////////////////////////////////////////
//
// Compile options needed: /GX
//
// next_permutation.cpp : Illustrates how to use the predicate version
//                        of the next_permutation function.
//
// Functions:
//
//    next_permutation : Change the order of the sequence to the
//                       next lexicograhic permutation.
//////////////////////////////////////////////////////////////////////

// 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> StrVector ;

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

    //Define an ostream iterator for strings
    typedef ostream_iterator<string> 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] = "K" ;
    Pattern[1] = "A" ;
    Pattern[2] = "L" ;

    //sort the contents of Pattern, required by next_permutation
    sort(start, end, less<string>()) ;

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

    // Generate all possible permutations

    cout << "After calling next_permutation...." << endl ;
    while ( next_permutation(start, end, less<string>()) )
    {
        copy(start, end, outIt) ;
        cout << endl ;
    }
}

 

Program Output is:

Before calling next_permutation:
Pattern: A K L

After calling next_permutation:.
A L K
K A L
K L A
L A K
L K A