TwistyPuzzleLib

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// Copyright 2023 Leszek Koltunski                                                               //

//                                                                                               //

// This file is part of Magic Cube.                                                              //

//                                                                                               //

// Magic Cube is proprietary software licensed under an EULA which you should have received      //

// along with the code. If not, check https://distorted.org/magic/License-Magic-Cube.html        //

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package org.distorted.objectlib.tablebases;

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public class TablebaseHelpers

{

  private static int swaps(int val, int[] buffer, int len)

    {

    int ret = 0;

    for(int i=0; i<len; i++)

      {

           if( buffer[i] >val ) ret++;

      else if( buffer[i]==val ) return ret;

      }

    return -1;

    }

///////////////////////////////////////////////////////////////////////////////////////////////////

  public static boolean permutationIsEven(int[] buffer)

    {

    int len = buffer.length;

    int numOfSwaps = 0;

    for(int i=0; i<len; i++) numOfSwaps += swaps(i,buffer,len);

    return (numOfSwaps%2==0);

    }

///////////////////////////////////////////////////////////////////////////////////////////////////

  public static int computeEvenPermutationNum(int[] permutation)

    {

    int len = permutation.length-2;

    int ret = 0;

    int mul = 4;

    for(int i=0; i<len; i++)

      {

      int n = swaps(len-1-i,permutation,len+2);

      ret += n;

      if( i<len-1 )

        {

        ret *= mul;

        mul++;

        }

      }

    return ret;

    }

///////////////////////////////////////////////////////////////////////////////////////////////////

  public static void getEvenPermutationFromNum(int[] buffer,int permSize, int permNum)

    {

    int index = permSize;

    int len = permSize-2;

    int totalSwaps = 0;

    for(int i=0; i<permSize; i++) buffer[i]=-1;

    for(int i=0; i<len; i++)

      {

      int swaps = (permNum%index);

      permNum /= index;

      index--;

      totalSwaps += swaps;

      for(int j=0; j<permSize; j++)

        {

        if( buffer[j]==-1 )

          {

          if( swaps==0 )

            {

            buffer[j] = i;

            break;

            }

          swaps--;

          }

        }

      }

    int lower, upper;

    if( (totalSwaps%2)==0 )

      {

      lower = permSize-2;

      upper = permSize-1;

      }

    else

      {

      lower = permSize-1;

      upper = permSize-2;

      }

    boolean first=true;

    for(int i=0; i<permSize; i++)

      if( buffer[i]==-1 )

        {

        if( first )

          {

          buffer[i] = lower;

          first=false;

          }

        else

          {

          buffer[i] = upper;

          break;

          }

        }

    }

}