combinations.hxx

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/*===========================================================================================================
 *
 * SHA - Simple Hybesis Algorithms
 *
 * 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/michael-jeulinl/Simple-Hybesis-Algorithms/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 SHA_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