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#!/usr/bin/perl
# https://perlweeklychallenge.org/blog/perl-weekly-challenge-020/
# Task #2
# Write a script to print the smallest pair of Amicable Numbers.
# For more information, please checkout wikipedia page.
# https://en.wikipedia.org/wiki/Amicable_numbers
use strict;
use warnings;
my $n = 0;
until (amicable(++$n)) {};
print "Smallest pair of Amicable Numbers: ($n,".amicable($n).")\n";
{
my %cache;
sub amicable {
my $n = shift;
$cache{$n} = sum(factors($n)) unless exists $cache{$n};
my $m = $cache{$n};
return if $m == $n; # same number
$cache{$m} = sum(factors($m)) unless exists $cache{$m};
return if $cache{$m} != $n; # not amicable
return $m;
}
}
sub sum {
my $s = 0;
$s += $_ for @_;
return $s;
}
sub factors {
my $n = shift;
my $upto = $n == 1 ? 1 : $n/2;
return grep {$n % $_ == 0} (1 .. $upto);
}
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