Challenge Accepted!

3 files changed, 71 insertions, 0 deletions

diff --git a/challenge-102/dave-jacoby/blog.txt b/challenge-102/dave-jacoby/blog.txt
new file mode 100644
index 0000000000..0461943e8b
--- /dev/null
+++ b/challenge-102/dave-jacoby/blog.txt
@@ -0,0 +1 @@
+https://jacoby.github.io/2021/03/01/rare-numbers-and-hash-perl-challenge-102.html
\ No newline at end of file
diff --git a/challenge-102/dave-jacoby/perl/ch-1.pl b/challenge-102/dave-jacoby/perl/ch-1.pl
new file mode 100644
index 0000000000..05d5ddad07
--- /dev/null
+++ b/challenge-102/dave-jacoby/perl/ch-1.pl
@@ -0,0 +1,44 @@
+#!/usr/bin/env perl
+
+use strict;
+use warnings;
+use feature qw{ postderef say signatures state };
+no warnings qw{ experimental };
+
+use Carp;
+
+my $i = shift @ARGV;
+$i //= 2;
+croak 'non-positive integer' if $i < 1;
+croak 'not an integer'       if $i =~ /\D/;
+
+say join "\n\t", "RARE NUMBERS: $i", rare_numbers($i), '';
+
+# a number r is "rare" when:
+#   - r1 is that number reversed
+#   - sqrt(r+r1) is an integer
+#   - sqrt(r-r1) is an integer
+sub rare_numbers ( $i ) {
+    my @output;
+
+    # given i == 5,
+    # low is 10000, the smallest five-digit number
+    # high is 99999, the highest five-digit number
+    my $low  = join '', map { $_ == 1 ? 1 : 0 } 1 .. $i;
+    my $high = 9 x $i;
+
+    for my $r ( $low .. $high ) {
+        my $r1 = reverse $r;
+        next if $r - $r1 < 0;    # early block for thing that break sqrt
+
+        my $s1 = sqrt( $r + $r1 );
+        next if $s1 =~ /\D/;     # test if integer
+
+        my $s2 = sqrt( $r - $r1 );
+        next if $s2 =~ /\D/;     # test if integer
+
+
+        push @output, $r;
+    }
+    return @output;
+}
diff --git a/challenge-102/dave-jacoby/perl/ch-2.pl b/challenge-102/dave-jacoby/perl/ch-2.pl
new file mode 100644
index 0000000000..630c256e61
--- /dev/null
+++ b/challenge-102/dave-jacoby/perl/ch-2.pl
@@ -0,0 +1,26 @@
+#!/usr/bin/env perl
+
+use strict;
+use warnings;
+use feature qw{ postderef say signatures state };
+no warnings qw{ experimental };
+
+use Carp;
+
+my $i = shift @ARGV;
+$i //= 2;
+croak 'non-positive integer' if $i < 1;
+croak 'not an integer'       if $i =~ /\D/;
+
+say join "\t", $i, hash_count($i);
+
+sub hash_count( $i ) {
+    my $output = '';
+    my $j      = $i;
+    while ( $j > 0 ) {
+        $output = '#' . $output;
+        $output = $j . $output if length $output < $i;
+        $j = $i - length $output;
+    }
+    return $output;
+}