1 files changed, 46 insertions, 0 deletions
diff --git a/challenge-153/lubos-kolouch/perl/ch-1.pl b/challenge-153/lubos-kolouch/perl/ch-1.pl
new file mode 100644
index 0000000000..eec490830a
--- /dev/null
+++ b/challenge-153/lubos-kolouch/perl/ch-1.pl
@@ -0,0 +1,46 @@
+use strict;
+use warnings;
+
+# keep seen factorials in a cache to speed things up
+my %fact_cache = (0 => 1);
+my %left_fact_cache; 
+
+sub calculate_factorial {
+    my $what = shift;
+
+    return $fact_cache{$what} if $fact_cache{$what};
+
+    # let's utilize the fact that we are processing the numbers in sequence
+    $fact_cache{$what} = $what * $fact_cache{$what-1};
+
+    return $fact_cache{$what};
+}
+
+sub calculate_left_fact {
+    my $what = shift;
+
+    return $left_fact_cache{$what} if $left_fact_cache{$what};
+
+    # let's utilize the fact that we are processing the numbers in sequence
+    $left_fact_cache{$what} = calculate_factorial($what-1) + $left_fact_cache{$what-1};
+
+    return $left_fact_cache{$what};
+}
+
+
+sub get_left_factorials {
+    my $what = shift;
+
+    my @output;
+
+    for (1..$what) {
+       push @output, calculate_left_fact($_);
+    }
+
+    return \@output;
+}
+
+use Test::More;
+
+is_deeply(get_left_factorials(10), [1, 2, 4, 10, 34, 154, 874, 5914, 46234, 409114]);
+done_testing;