package io.github.skenvy;
   
   import java.util.ArrayList;
   import java.util.List;
   
   /**
    * A collection of cells ~ can be a row, column, or box|region|block.
    */
   public class CellCollection {
  
    private final List<Cell> cells;
  
    /**
     * Initialise an empty collection to reference 9 cells in a row, column, or box.
     */
    public CellCollection() {
      this.cells = new ArrayList<Cell>(9);
    }
  
    /**
     * Initialise an empty collection to reference N*N cells in a row, column, or box.
     */
    public CellCollection(int boardSize) {
      this.cells = new ArrayList<Cell>((boardSize * boardSize));
    }
  
    /**
     * Get a collection of the cells.
     */
    public List<Cell> getCells() {
      // Return new list instance to prevent removal from underlying collection.
      return new ArrayList<Cell>(this.cells);
    }
  
    public void addCellToCollection(Cell cell) {
      this.cells.add(cell);
    }
  
    public int[] getValues() {
      int[] values = new int[this.cells.size()];
      for (int k = 0; k < this.cells.size(); k++) {
        values[k] = this.cells.get(k).getValue();
      }
      return values;
    }
  
    /**
     * Used for cell collection related exceptions.
     */
    public class SudokuCellCollectionException extends Exception {
  
      public SudokuCellCollectionException(String string) {
        super(string);
      }
  
    }
  
  }