1 files changed, 54 insertions, 0 deletions
diff --git a/challenge-119/dave-jacoby/perl/ch-2.pl b/challenge-119/dave-jacoby/perl/ch-2.pl
new file mode 100644
index 0000000000..702ef4b13a
--- /dev/null
+++ b/challenge-119/dave-jacoby/perl/ch-2.pl
@@ -0,0 +1,54 @@
+#!/usr/bin/env perl
+
+use strict;
+use warnings;
+use feature qw{ postderef say signatures state };
+no warnings qw{ experimental };
+
+use Memoize;
+memoize('first_pass');
+
+my @list = map { int } @ARGV;
+@list = ( 2, 5, 10, 60, 200 ) unless scalar @list;
+
+for my $n (@list) {
+    say join "\t", '', $n, solve_sequence($n);
+}
+
+# here we get an array such that index $n is in the array
+# using increasingly aggressive methods, then 
+sub solve_sequence( $n ) {
+    my $j        = $n * 2;
+    my @sequence = get_sequence( 1 .. $j );
+    while ( !$sequence[$n] ) {
+        $j        = $j * 2;
+        @sequence = get_sequence( 1 .. $j );
+    }
+    return $sequence[$n];
+}
+
+# the next things we want to do are to remove the blocked numbers
+# which contain either 0 or 11, and then add another entry to the
+# start of the array so that 1 aligns with 1.
+sub get_sequence( @arr ) {
+    my @seq =
+        grep { !/11/ }
+        grep { !/0/ }
+        map  { first_pass($_) } @arr;
+    unshift @seq, '';
+    return @seq;
+}
+
+# the numbers will contain only the digits 1, 2 and 3, so to limit 
+# the amount of numbers we have to come up with, I first make everything
+# base 4. This function is memoizable and so I memoized it.
+sub first_pass ( $n ) {
+    return $n if $n == 0;
+    my @output;
+    while ($n) {
+        my $i = $n % 4;
+        $n = int $n / 4;
+        push @output, $i;
+    }
+    return join '', reverse @output;
+}