Board.groovy

Cell[] getRecord(int rowNum) { return board[rowNum] }

Cell[] getColumn(int colNum) { return (0..<board.length).collect { board[it][colNum] } }

Cell[] getSquare(int rowNum, int colNum) {
    int beginRow = rowNum - rowNum % 3
    int beginColumn = colNum - colNum % 3

    return (beginRow..<beginRow + 3).collect { row ->
        (beginColumn..<beginColumn + 3).collect { column ->
            board[row][column]
        }
    }.flatten()
}