SpiralThroughA2DArray.java

/*license*\
   XBN-Java: Copyright (C) 2014, Jeff Epstein (aliteralmind __DASH__ github __AT__ yahoo __DOT__ com)

   This software is dual-licensed under the:
   - Lesser General Public License (LGPL) version 3.0 or, at your option, any later version;
   - Apache Software License (ASL) version 2.0.

   Either license may be applied at your discretion. More information may be found at
   - http://en.wikipedia.org/wiki/Multi-licensing.

   The text of both licenses is available in the root directory of this project, under the names "LICENSE_lgpl-3.0.txt" and "LICENSE_asl-2.0.txt". The latest copies may be downloaded at:
   - LGPL 3.0: https://www.gnu.org/licenses/lgpl-3.0.txt
   - ASL 2.0: http://www.apache.org/licenses/LICENSE-2.0.txt
\*license*/
package  com.github.xbn.examples.lang.non_xbn;
   import  java.util.NoSuchElementException;
/**
   <p>Uses an iterator-like object to move through a two-dimensional array, starting from the top, left-to-right, down, right-to-left, down, left-to-right, ...</p>

   <p>{@code java com.github.xbn.examples.lang.non_xbn.SpiralThroughA2DArray}</p>
 **/
public class SpiralThroughA2DArray  {
   public static final void main(String[] ignored)  {
      int rows = 10;
      int cols = 10;
      int[][] boardPositions = new int[rows][cols];

      SpiralGridPositionIterator gridPosItr = new SpiralGridPositionIterator(rows, cols);

      int positionNum = rows * cols;  //Start at max and descend

      //Fill the array
         while(gridPosItr.hasNext())  {
            gridPosItr.goToNext();
            //System.out.println("[" + gridPosItr.getRowIdx() + "," + gridPosItr.getColIdx() + "]=" + positionNum);
            boardPositions[gridPosItr.getRowIdx()][gridPosItr.getColIdx()] = positionNum--;
         }

      //Display
         for(int rowIdx = 0; rowIdx < rows; rowIdx++)  {
            for(int colIdx = 0; colIdx < cols; colIdx++)  {
               System.out.print(boardPositions[rowIdx][colIdx] + " ");
            }
            System.out.println();
         }
   }
}

class SpiralGridPositionIterator  {
//config
   public final int rows;
   public final int cols;
//state
   private int rowIdx;
   private int colIdx;
   private boolean isColIdxAsc;
//internal
   private final int colsMinus1;
   private final int rowsMinus1;

   public SpiralGridPositionIterator(int rows, int cols)  {
      this.rows = rows;
      this.cols = cols;

      colIdx = -1;  //MUST initialize to -1  (See "First time is a special case")
      rowIdx = 0;

      isColIdxAsc = true;
      colsMinus1 = cols - 1;
      rowsMinus1 = rows - 1;
   }
   public boolean hasNext()  {
      if(getRowIdx() < rowsMinus1)  {
         return  true;
      }
      return  (isColIdxAsc
            ?  getColIdx() < colsMinus1
            :  getColIdx() > 0);
   }
   public void goToNext()  {
      if(colIdx == -1)  {
         //First time is a special case.  (See "MUST initialize to -1")
         colIdx = 0;
         rowIdx = 0;
         return;
      }
      if(!hasNext())  {
         throw  new NoSuchElementException();
      }

      if(isColIdxAsc)  {
         if(getColIdx() < colsMinus1)  {
            colIdx++;
         }  else  {

            //In last column
            isColIdxAsc = !isColIdxAsc;
            rowIdx++;
         }

      //ELSE: Descending
      }  else if(getColIdx() > 0) {
         colIdx--;

      }  else  {

         //In first column
         isColIdxAsc = !isColIdxAsc;
         rowIdx++;
      }
   }
   public int getRowIdx()  {
      return  rowIdx;
   }
   public int getColIdx()  {
      return  colIdx;
   }
}