challenge-056/mark-anderson/perl/ch-1.pl


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#!/usr/bin/env perl
use Modern::Perl;
use Algorithm::Combinatorics 'combinations';
use List::Util 'all';

# Usage:   perl ch-1.pl @N $k
# Example: perl ch-1.pl 2 7 9 2
# Output:  2,1

die "Usage: perl ch-1.pl \@N \$k" unless all { /\A\d+\z/ } @ARGV;
 
my $k = pop @ARGV;

my $combo = combinations([keys @ARGV], 2);

while (my $indices = $combo->next) {
    my ($i, $j) = $indices->@*;
    say "$j,$i" if $ARGV[$j] - $ARGV[$i] == $k;
}