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package com.hfg.math;


import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.List;

import com.hfg.util.collection.CollectionUtil;

//------------------------------------------------------------------------------
/**
 Utility functions for creating permutations.
 Permutations are for lists (order matters) and combinations are for groups (order doesn’t matter).
 
 @author J. Alex Taylor, hairyfatguy.com
 
 */
//------------------------------------------------------------------------------
// com.hfg Library
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
//
// J. Alex Taylor, President, Founder, CEO, COO, CFO, OOPS hairyfatguy.com
// [email protected]
//------------------------------------------------------------------------------


public class Permutations
{
   //---------------------------------------------------------------------------
   public static List permutationsWithRepetition(List inObjects, int inPermutationSize)
   {
      List combinations = null;

      if (CollectionUtil.hasValues(inObjects))
      {
         if (inPermutationSize == 1)
         {
            // Special case if permutation size is 1
            combinations = new ArrayList<>(inObjects.size());
            for (T obj : inObjects)
            {
               T[] combination = (T[]) Array.newInstance(inObjects.get(0).getClass(), inPermutationSize);
               combination[0] = obj;
               combinations.add(combination);
            }
         }
         else
         {
            int numCombinations = (int) Math.pow(inObjects.size(), inPermutationSize);
            combinations = new ArrayList<>(numCombinations);

            innerPermutationsWithRepetition(inObjects, (T[]) Array.newInstance(inObjects.get(0).getClass(), inPermutationSize), 0, combinations);
         }
      }
      return combinations;
   }

   //---------------------------------------------------------------------------
   private static  void innerPermutationsWithRepetition(List inObjects, T[] inArray, int inCurrentIndex, List inPermutations)
   {
      if (inCurrentIndex < inArray.length)
      {
         for (int i = 0; i < inObjects.size(); i++)
         {
            T[] oldArray = inArray.clone();
            inArray[inCurrentIndex] = inObjects.get(i);
            innerPermutationsWithRepetition(inObjects, inArray, inCurrentIndex + 1, inPermutations);
            inArray = oldArray;
         }
      }
      else
      {
         inPermutations.add(inArray);
      }
   }
}