From f5f9c8a7c5b5e6e640c6e52579878e0ed5cc97fa Mon Sep 17 00:00:00 2001
From: Dave Jacoby <jacoby.david@gmail.com>
Date: Mon, 10 Jan 2022 19:44:04 -0500
Subject: 147 - 3 * 7 * 7

---
 challenge-147/dave-jacoby/perl/ch-1.pl | 35 ++++++++++++++++++++++++++++++++
 challenge-147/dave-jacoby/perl/ch-2.pl | 37 ++++++++++++++++++++++++++++++++++
 2 files changed, 72 insertions(+)
 create mode 100644 challenge-147/dave-jacoby/perl/ch-1.pl
 create mode 100644 challenge-147/dave-jacoby/perl/ch-2.pl

diff --git a/challenge-147/dave-jacoby/perl/ch-1.pl b/challenge-147/dave-jacoby/perl/ch-1.pl
new file mode 100644
index 0000000000..edc998ee77
--- /dev/null
+++ b/challenge-147/dave-jacoby/perl/ch-1.pl
@@ -0,0 +1,35 @@
+#!/usr/bin/env perl
+
+use strict;
+use warnings;
+use feature qw{ say postderef signatures state };
+no warnings qw{ experimental };
+
+my %primes;
+my %trunc;
+my $c = 1;
+my $n = 2;
+
+while (1) {
+    if ( is_prime($n) ) {
+        $primes{$n}++;
+        my $copy = $n;
+        while ( length $copy > 0 ) {
+            last unless $primes{$copy};
+            substr( $copy, 0, 1 ) = '';
+            if ( $copy eq '' ) {
+                $trunc{$n}++ if $copy eq '';
+                last;
+            }
+        }
+        last if scalar keys %trunc > 20;
+    }
+    $n++;
+}
+
+say join ', ', sort { $a <=> $b } keys %trunc;
+
+sub is_prime ($n) {
+    for ( 2 .. sqrt $n ) { return unless $n % $_ }
+    return 1;
+}
diff --git a/challenge-147/dave-jacoby/perl/ch-2.pl b/challenge-147/dave-jacoby/perl/ch-2.pl
new file mode 100644
index 0000000000..4385f57450
--- /dev/null
+++ b/challenge-147/dave-jacoby/perl/ch-2.pl
@@ -0,0 +1,37 @@
+#!/usr/bin/env perl
+
+use strict;
+use warnings;
+use feature qw{ say postderef signatures state };
+no warnings qw{ experimental };
+
+my $top      = 100_000;
+my @pentagon = map { pentagon($_) } 0 .. $top;
+my %pentagon = map { $_ => 1 } @pentagon;
+
+for my $i ( 1 .. $top ) {
+    for my $j ( 1 .. $i - 1 ) {
+        my $pi  = $pentagon[$i];
+        my $pj  = $pentagon[$j];
+        my $sum = $pi + $pj;
+
+        if ( $pentagon{$sum} ) {
+            my $product = abs( $pi - $pj );
+            if ( $pentagon{$product} ) {
+                say <<"END";
+        P($i) = $pi
+        P($j) = $pj
+        $pi + $pj = $sum
+        abs( $pi - $pj ) = $product
+END
+                exit;
+
+            }
+        }
+
+    }
+}
+
+sub pentagon ( $n ) {
+    return $n * ( ( $n * 3 ) - 1 ) / 2;
+}
-- 
cgit 


From 9b1f239ffecd7923ede7ba8d965939fd08fb5661 Mon Sep 17 00:00:00 2001
From: Dave Jacoby <jacoby.david@gmail.com>
Date: Tue, 11 Jan 2022 17:48:03 -0500
Subject: Revise and extend my code, added blog

---
 challenge-147/dave-jacoby/blog.txt     | 1 +
 challenge-147/dave-jacoby/perl/ch-1.pl | 4 ++--
 challenge-147/dave-jacoby/perl/ch-2.pl | 8 +++-----
 3 files changed, 6 insertions(+), 7 deletions(-)
 create mode 100644 challenge-147/dave-jacoby/blog.txt

diff --git a/challenge-147/dave-jacoby/blog.txt b/challenge-147/dave-jacoby/blog.txt
new file mode 100644
index 0000000000..e386698c3c
--- /dev/null
+++ b/challenge-147/dave-jacoby/blog.txt
@@ -0,0 +1 @@
+https://jacoby.github.io/2022/01/11/truncations-and-pentagons-the-weekly-challenge-147.html
\ No newline at end of file
diff --git a/challenge-147/dave-jacoby/perl/ch-1.pl b/challenge-147/dave-jacoby/perl/ch-1.pl
index edc998ee77..197c72f5b7 100644
--- a/challenge-147/dave-jacoby/perl/ch-1.pl
+++ b/challenge-147/dave-jacoby/perl/ch-1.pl
@@ -11,7 +11,7 @@ my $c = 1;
 my $n = 2;
 
 while (1) {
-    if ( is_prime($n) ) {
+    if ( $n !~ /0/mx && is_prime($n) ) {
         $primes{$n}++;
         my $copy = $n;
         while ( length $copy > 0 ) {
@@ -22,7 +22,7 @@ while (1) {
                 last;
             }
         }
-        last if scalar keys %trunc > 20;
+        last if scalar keys %trunc > 30;
     }
     $n++;
 }
diff --git a/challenge-147/dave-jacoby/perl/ch-2.pl b/challenge-147/dave-jacoby/perl/ch-2.pl
index 4385f57450..61f3b1b1d6 100644
--- a/challenge-147/dave-jacoby/perl/ch-2.pl
+++ b/challenge-147/dave-jacoby/perl/ch-2.pl
@@ -5,16 +5,16 @@ use warnings;
 use feature qw{ say postderef signatures state };
 no warnings qw{ experimental };
 
-my $top      = 100_000;
+my $top      = 10_000;
 my @pentagon = map { pentagon($_) } 0 .. $top;
 my %pentagon = map { $_ => 1 } @pentagon;
+delete $pentagon{0};
 
 for my $i ( 1 .. $top ) {
-    for my $j ( 1 .. $i - 1 ) {
+    for my $j ( 1 .. $i  ) {
         my $pi  = $pentagon[$i];
         my $pj  = $pentagon[$j];
         my $sum = $pi + $pj;
-
         if ( $pentagon{$sum} ) {
             my $product = abs( $pi - $pj );
             if ( $pentagon{$product} ) {
@@ -25,10 +25,8 @@ for my $i ( 1 .. $top ) {
         abs( $pi - $pj ) = $product
 END
                 exit;
-
             }
         }
-
     }
 }
 
-- 
cgit