Board.java

package crossnum;

import java.util.List;
import java.util.stream.Collectors;

/**
 * Represents a square grid with each cell containing a digit or blank.
 *
 * @author dub_nerd
 *
 */
public class Board {

    /**
     * Each grid entry is represented as a 'Variable'. We store them in a flat
     * list -- see the get(row,col) method to see how they are accessed as a
     * grid.
     */
    private final List<Variable> variables;


    /**
     * Length of a side of the grid, i.e. the square root of the number of
     * entries.
     */
    private final int side;


    /**
     * Constructor for the Board class. For convenience of representation, it is
     * initialised from a character String representing the cells of the grid in
     * order. The string must have a perfect square number of characters.
     *
     * @param s
     *            input String.
     */
    Board(String s) {

        // Ensure grid is square
        side = (int) Math.sqrt(s.length());
        if (s.length() != (side * side)) {
            throw new RuntimeException("Board not square");
        }

        /*
         * Map the input characters to Variables. Each Variable gets the
         * character's digit value, or zero if blank.
         */
        variables = s.chars()
                .mapToObj(c -> new Variable(c == ' ' ? 0 : c - '0'))
                .collect(Collectors.toList());

    }


    /**
     * Get the Variable at the specified row and column.
     * @param row the row
     * @param col the column
     * @return the Variable at the specified row and column.
     */
    Variable get(int row, int col) {
        int index = row * getSide() + col;
        return variables.get(index);
    }


    /**
     * Get the length of the board's side, i.e the square root of the
     * number of cells.
     * @return length of side.
     */
    public int getSide() {
        return side;
    }


}