https://theweeklychallenge.org/blog/perl-weekly-challenge-175/

2 files changed, 37 insertions, 0 deletions

diff --git a/challenge-175/kjetillll/perl/ch-1.pl b/challenge-175/kjetillll/perl/ch-1.pl
new file mode 100644
index 0000000000..5137aca00d
--- /dev/null
+++ b/challenge-175/kjetillll/perl/ch-1.pl
@@ -0,0 +1,10 @@
+#!/usr/bin/perl
+use Time::Local;
+my $y = shift || 1900+(localtime)[5];
+for my $m (1..12){
+    for(reverse 1..31){
+	is_sunday($y,$m,$_) and printf("%04d-%02d-%02d\n", $y, $m, $_) and last
+    }
+}
+
+sub is_sunday{ my($y,$m,$d)=@_; (eval{ timegm(0,0,0,$d,$m-1,$y) } / 86400 - 3) % 7 == 0 }
diff --git a/challenge-175/kjetillll/perl/ch-2.pl b/challenge-175/kjetillll/perl/ch-2.pl
new file mode 100644
index 0000000000..5dc7946afe
--- /dev/null
+++ b/challenge-175/kjetillll/perl/ch-2.pl
@@ -0,0 +1,27 @@
+#!/usr/bin/perl
+# prints the first 20 Perfect Totient Numbers:
+# 3 9 15 27 39 81 111 183 243 255 327 363 471 729 2187
+# https://theweeklychallenge.org/blog/perl-weekly-challenge-175/
+# https://en.wikipedia.org/wiki/Perfect_totient_number
+# use Math::Prime::Util::GMP 'gcd';     # ...is faster, but not a core module
+# use Math::Prime::Util::GMP 'totient'; # ...is screamingly fast!
+
+use strict; use warnings;
+use Memoize;
+memoize('totient');  #good idea, unless using GMP
+#memoize('gcd');     #bad idea, runs slower
+
+sub totient { my $n=shift; 0+grep gcd($_,$n)==1, 1..$n-1 }
+
+sub gcd { my($a,$b)=@_;($a,$b)=($b,$a)if$a>$b;($a,$b)=($b%$a,$a)while$a;$b }
+
+my $want = shift() // 20;
+my $try = 1;
+while( $want > 0 ){
+    my $sum = 0;
+    my $n = $try;
+    $sum += $n = totient($n) while $n>1;
+    print "$try\n" and $want-- if $sum == $try;
+    $try+=2;
+}
+