permutations.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_PERMUTATIONS_HXX
#define MODULE_COMBINATORY_PERMUTATIONS_HXX

// STD includes
#include <list>

namespace SHA_Combinatory
{
  template <typename Container, typename IT>
  std::list<Container> Permutations(const IT& begin, const IT& end)
  {
    std::list<Container> permutations; // Contains the output permutations

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

    // Recusion termination - Unique element
    if (kSeqSize == 1)
    {
      Container elementContainer;
      elementContainer.push_back(*begin);
      permutations.push_back(elementContainer);
      return permutations;
    }

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

    // Put the letter into every possible position of the existing permutations.
    Container currentPermutation;
    for (auto it = subPermutations.begin(); it != subPermutations.end(); ++it)
      for (int i = 0; i < kSeqSize; ++i)
      {
        currentPermutation = *it;
        currentPermutation.insert(currentPermutation.begin() + i, *begin);
        permutations.push_back(currentPermutation);
      }

    return permutations;
  }
}

#endif // MODULE_COMBINATORY_PERMUTATIONS_HXX