combinations algorithm

Question

I want to make simple sorting algorithm.

given the input \"abcde\", I would like the output below. could you tell me the algorithm for that?

arr[0] =         


        

Answer 1

In C++ given the following routine:

template 
bool next_combination(const Iterator first, Iterator k, const Iterator last)
{
   /* Credits: Mark Nelson http://marknelson.us */
   if ((first == last) || (first == k) || (last == k))
      return false;
   Iterator i1 = first;
   Iterator i2 = last;
   ++i1;
   if (last == i1)
      return false;
   i1 = last;
   --i1;
   i1 = k;
   --i2;
   while (first != i1)
   {
      if (*--i1 < *i2)
      {
         Iterator j = k;
         while (!(*i1 < *j)) ++j;
         std::iter_swap(i1,j);
         ++i1;
         ++j;
         i2 = k;
         std::rotate(i1,j,last);
         while (last != j)
         {
            ++j;
            ++i2;
         }
         std::rotate(k,i2,last);
         return true;
      }
   }
   std::rotate(first,k,last);
   return false;
}

You can then proceed to do the following:

std::string s = "abcde";
for(std::size_t i = 1; i != s.size(); ++i)
{
   do
   {
      std::cout << std::string(s.begin(),s.begin() + i) << std::endl;
   }
   while(next_combination(s.begin(),s.begin() + i,s.end()));
}

Note: That you should expect to see 2^n-1 combinations, where n is the length of the array or string.