push changes to chowla so that we can compare performances with Benchmark

1 files changed, 51 insertions, 7 deletions

diff --git a/challenge-109/james-smith/perl/ch-1.pl b/challenge-109/james-smith/perl/ch-1.pl
index 2c38afe0c4..1b89226a6a 100644
--- a/challenge-109/james-smith/perl/ch-1.pl
+++ b/challenge-109/james-smith/perl/ch-1.pl
@@ -5,18 +5,62 @@ use strict;
 use warnings;
 use feature qw(say);
 use Test::More;
+use Benchmark qw(cmpthese);
 
-my @answer = (9999, 0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21);
+my @answer = qw(9999
+  0  0  0  2  0  5  0  6  3  7
+  0 15  0  9  8 14  0 20  0 21
+);
 
 
-is( chowla($_), $answer[ $_ ] ) foreach 1..20;
+is( chowla_map($_), $answer[ $_ ] ) foreach 1..20;
+is( chowla_for($_), $answer[ $_ ] ) foreach 1..20;
 
 done_testing();
 
-sub my_function {
-  sub chowla {
-    my ($t,$n) = (0,@_);
-    return ( map { (($n%$_) || ($t+=$_)) && () } 2..$n-1 ), $t;
-  }
+## We will quickly run benchmarking...
+## This suggests the for loop to be approximately 40-50%
+## faster than the map solution...
+## It is also 9 characters shorter...
+
+cmpthese(1_000_000, {
+  'Map' => sub { chowla_map($_) foreach 1..20; },
+  'For' => sub { chowla_for($_) foreach 1..20; },
+});
+
+##
+##        Rate  Map  For
+## Map 38670/s   -- -33%
+## For 57670/s  49%   --
+##
+
+sub chowla_map {
+  my ($t,$n) = (0,@_);
+## First attempt - the one-liner is to write this as a map,
+## we add $t at the end which is the value returned
+  ( map { (($n%$_) || ($t+=$_)) && () } 2..$n-1 ), $t;
+}
+
+sub chowla_for {
+  my($t,$n)=(0,@_);
+
+  ## This time we won't write this as a nasty map/reduce solution...
+  ##
+  ## Just a for loop;
+  ##
+  ## Notes:
+  ##  * To allow for an "unless" in a postfix loop, we rewrite this
+  ##    by noting:
+  ##      unless( $condition ) { fun(); }
+  ##    can be rewritten as:
+  ##      ($condition)||($fun())
+  ##  * in perl `foreach` and `for` are synonymous - so we can shorten
+
+  ($n%$_)||($t+=$_) for 2..$n-1;
+
+  ## Now a quick "shortening" - if there is no specific return
+  ## statement - we can just omit the return in the last statement...
+
+  $t;
 }