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#!/usr/bin/perl
use Modern::Perl;
use Math::Prime::Util qw(is_prime);
# https://perlweeklychallenge.org/blog/perl-weekly-challenge-015/
# Write a script to generate first 10 strong and weak prime numbers.
#
# For example, the nth prime number is represented by p(n).
#
# p(1) = 2
# p(2) = 3
# p(3) = 5
# p(4) = 7
# p(5) = 11
#
# Strong Prime number p(n) when p(n) > [ p(n-1) + p(n+1) ] / 2
# Weak Prime number p(n) when p(n) < [ p(n-1) + p(n+1) ] / 2
#
my $limit = shift || 10;
my @weak;
my @strong;
my @balanced;
my $p = 5;
my @primes = (2,3,$p);
my ($l,$m,$r) = @primes;
while (@weak < $limit or @strong < $limit) {
$p+=2;
next unless is_prime($p);
push @primes, $p;
if (($l+$r)/2 < $m) {
push @strong, $m;
} elsif (($l+$r)/2 > $m) {
push @weak, $m;
} else {
push @balanced, $m;
}
($l,$m,$r) = ($m,$r,$p);
}
say "primes: " . join(",", @primes);
say "weak primes: " . join(",", @weak);
say "balanced primes: " . join(",", @balanced);
say "strong primes: " . join(",", @strong);
__END__
perl -MCPAN -e 'install Math::Prime::Util'
./ch1.pl
primes: 2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97,101,103
weak primes: 3,7,13,19,23,31,43,47,61,73,83,89
balanced primes: 5,53
strong primes: 11,17,29,37,41,59,67,71,79,97
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