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use v6;
################################################################################
=begin comment
Perl Weekly Challenge 023
=========================
Task #1
-------
Create a script that prints nth order forward difference series. You should be a
able to pass the list of numbers and order number as command line parameters.
Let me show you with an example.
Suppose we have list (X) of numbers: 5, 9, 2, 8, 1, 6 and we would like to
create 1st order forward difference series (Y). So using the formula Y(i) =
X(i+1) - X(i), we get the following numbers: (9-5), (2-9), (8-2), (1-8),
(6-1). In short, the final series would be: 4, -7, 6, -7, 5. If you noticed,
it has one less number than the original series. Similary you can carry on 2nd
order forward difference series like: (-7-4), (6+7), (-7-6), (5+7) => -11, 13,
-13, 12.
=end comment
################################################################################
#--------------------------------------#
# Copyright © 2019 PerlMonk Athanasius #
#--------------------------------------#
my UInt:D constant $ORDER = 1;
BEGIN say '';
#===============================================================================
sub MAIN(*@series, UInt:D :$order = $ORDER)
#===============================================================================
{
check-arguments(@series, $order);
for 1 .. $order
{
my UInt $max-index = @series.elems - 1;
my @new-series;
@new-series.push(@series[$_] - @series[$_ - 1]) for 1 .. $max-index;
@series = @new-series;
}
"%s order forward difference series:\n(%s)\n".printf:
ordinal($order), join(', ', @series);
CATCH
{
default
{
$*ERR.say: .message ~ "\n" ~ $*USAGE;
}
}
}
#-------------------------------------------------------------------------------
sub check-arguments(@series, UInt:D $order)
#-------------------------------------------------------------------------------
{
my UInt $elements = @series.elems;
$elements > 1
or die "Invalid number of elements ($elements) in the series: must " ~
"be at least 2";
$order > 0
or die "Invalid order ($order): must be an integer > 0";
$order < $elements
or die "Invalid order ($order): a series of $elements elements " ~
"cannot have an order > { $elements - 1 }";
}
#-------------------------------------------------------------------------------
sub ordinal(UInt:D $cardinal)
#-------------------------------------------------------------------------------
{
my $suffix = 'th';
my $digit_0 = $cardinal % 10;
my $digit_1 = ($cardinal / 10).floor % 10;
if ($digit_1 != 1)
{
$suffix = $digit_0 == 1 ?? 'st' !!
$digit_0 == 2 ?? 'nd' !!
$digit_0 == 3 ?? 'rd' !! 'th';
}
return $cardinal ~ $suffix;
}
################################################################################
|
