combinations.hxx

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/*===========================================================================================================
 *
 * HUC - Hurna Core
 *
 * Copyright (c) Michael Jeulin-Lagarrigue
 *
 *  Licensed under the MIT License, you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *         https://github.com/Hurna/Hurna-Core/blob/master/LICENSE
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License is
 * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and limitations under the License.
 *
 * The above copyright notice and this permission notice shall be included in all copies or
 * substantial portions of the Software.
 *
 *=========================================================================================================*/
#ifndef MODULE_COMBINATORY_COMBINATIONS_HXX
#define MODULE_COMBINATORY_COMBINATIONS_HXX

// STD includes
#include <list>

namespace huc
{
  namespace combinatory
  {
    template <typename Container, typename IT>
    std::list<Container> Combinations(const IT& begin, const IT& end)
    {
      std::list<Container> combinations;

      // Recusion termination
      const auto kSeqSize = static_cast<const int>(std::distance(begin, end));
      if (kSeqSize <= 0)
        return combinations;

      // Keep first element
      Container elementContainer;
      elementContainer.push_back(*begin);
      combinations.push_back(elementContainer);

      // Recursion termination
      if (kSeqSize == 1)
        return combinations;

      // Build all permutations of the suffix - Recursion
      auto subCombinations = Combinations<Container, IT>(begin + 1, end);

      // Put the letter into every possible position of the existing permutations.
      for (auto it = subCombinations.begin(); it != subCombinations.end(); ++it)
      {
        combinations.push_back(*it);
        it->push_back(*begin);
        combinations.push_back(*it);
      }

      return combinations;
    }
  }
}

#endif // MODULE_COMBINATORY_COMBINATIONS_HXX