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Implementing Permutation Variations

, 14 Jul 2004 CPOL 65.8K 780 24
Several enhanced permutation algorithms created in iterative or recursive solution.
// ============================================================================
// File:   StlPermu.cpp - Testing StlPermutation
// Author:   Zuoliu Ding, May 2004
// ============================================================================
#include <string>
#include <vector>
#include <algorithm>
#include <map>
using namespace std;

typedef map<char, int> Position_Map;
typedef pair<char, int> Position_Pair;


// STL: TEMPLATE FUNCTION next_permutation in algorithm standard header
// permute and test for pure ascending, using operator<
template<class _BidIt> inline
bool _next_permutation(_BidIt _First, _BidIt _Last, 
                       Position_Map* pMap/*=NULL*/)
{   
   _BidIt _Next = _Last;
   if (_First ==_Last || _First == --_Next) return (false);

   for (; ; )
   {   
      _BidIt _Next1 = _Next;
      if (pMap? (*pMap)[*--_Next] < (*pMap)[*_Next1]: 
                *--_Next < *_Next1)      
      {   
         _BidIt _Mid = _Last;
         for (; !(pMap? (*pMap)[*_Next] < (*pMap)[*--_Mid]: 
                        *_Next < *--_Mid);); 

         std::iter_swap(_Next, _Mid);
         std::reverse(_Next1, _Last);   
         return (true);
      }

      if (_Next == _First)
      {   
         std::reverse(_First, _Last);
         return (false);
      }
   }
}

// ============================================================================
// Function:   StlPermutation - using STL function next_permutation
// Description: Generate all Permuted strings for an input string
// Parameter:   sz:   [in] an input string.
// Return:      A vector of all Permuted strings.
// Note:      STL next_permutation permutes the string sz to the 
//            lexicographically next string as an arrangement, and then 
//            returns true. If the string sz is in descending order then 
//            it returns false.
// ============================================================================
vector<string> StlPermutation(const char* sz, 
                              bool bOrdered/*=true*/)
{
   vector<string> v;
   string s = sz;
   Position_Map mapPos;

   if (!bOrdered)
      for (unsigned int i=0; i<s.length(); i++)
         mapPos.insert(Position_Pair(s[i], i));   

   do   v.insert(v.end(), s);   
   while (_next_permutation(s.begin(), s.end(), 
                            bOrdered? NULL: &mapPos)); 

   return v;
}

/*
template<class _BidIt> inline
bool _next_permutation(_BidIt _First, _BidIt _Last)
{   
   _BidIt _Next = _Last;
   if (_First ==_Last || _First == --_Next) return (false);

   for (; ; )
   {   // find rightmost element smaller than successor
      _BidIt _Next1 = _Next;
      if (*--_Next < *_Next1)      
      {   // swap with rightmost element that's smaller
         _BidIt _Mid = _Last;
         for (; !(*_Next < *--_Mid);) ;

         std::iter_swap(_Next, _Mid);
         std::reverse(_Next1, _Last);   
         return (true);
      }

      if (_Next == _First)
      {   // pure descending, flip all
         std::reverse(_First, _Last);
         return (false);
      }
   }
}

vector<string> StlPermutation(const char* sz)
{
   vector<string> v;
   string s = sz;

   do   v.insert(v.end(), s);   
   while (_next_permutation(s.begin(), s.end())); 

   return v;
}
*/

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About the Author

Zuoliu Ding
Software Developer
United States United States
An Adjunct Faculty and Software Developer in Los Angeles and Orange County, CA

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