newer more compact version of smith numbers

1 files changed, 32 insertions, 36 deletions

diff --git a/challenge-133/james-smith/perl/ch-2.pl b/challenge-133/james-smith/perl/ch-2.pl
index 5f7bed5d67..6163b97940 100644
--- a/challenge-133/james-smith/perl/ch-2.pl
+++ b/challenge-133/james-smith/perl/ch-2.pl
@@ -4,46 +4,42 @@ use strict;
 
 use warnings;
 use feature qw(say);
-use Data::Dumper qw(Dumper);
-
-my @primes    = (2,3);
-my %ds;
-my %comp;
-my @t =  smith_numbers(@ARGV?$ARGV[0]:100);
-print "@t\n";
-
-sub smith_numbers {
-  my $C = shift;
-  my @sn = ();
-  my $n = 4;
-  while(1) {
-    my @q = prime_factors($n);
-    if( @q ) {
-      my $t = sum_digits($n);
-      $t-= sum_digits($_) foreach @q;
-      unless($t) {
-        push @sn, $n;
-        return @sn if @sn==$C;
-      }
-    }
-    $n++;
-  }
-}
 
-sub sum_digits {
-  return $ds{$_[0]} if exists $ds{$_[0]};
-  my $t = 0;
-  $t+= $_ foreach split //, $_[0];
-  return $ds{$_[0]} = $t;
-}
+my(@primes,%ds,%comp) = (2,3);
+say $_ foreach smith_numbers(@ARGV?$ARGV[0]:100);
+#say $_ foreach smith_numbers_readable(@ARGV?$ARGV[0]:100);
+
+sub sum {        my $t = 0; $t+=$_ foreach @_; $t; }
+sub sum_digits { return $ds{$_[0]} ||= sum split //, $_[0]; }
 
 sub prime_factors {
   my $N = shift;
-  my @factors;
-  foreach (@primes) {
-    return @{ $comp{$N} = [ $_, exists $comp{$N/$_}? @{$comp{$N/$_}} : $N/$_ ] } unless $N % $_;
-  }
-  push @primes,$N;
+
+  ## If we are composite then store the factors for the composite and return...
+  ( $N % $_) or ( return @{ $comp{$N} = [ $_, @{$comp{ $N / $_ }||[$N/$_]}] } ) foreach @primes;
+
+  ## Otherwise we are prime so add to primes and return nothing....
+  push @primes, $N;
   return;
 }
 
+sub smith_numbers_readable {
+  my ( $C, $n, @sn ) = (shift,3);
+  while($n++) { ## $n starts at 4 ... lowest possible smith number is 4 ( composite or 2 x 2 )
+    next unless my @q = prime_factors($n); ## Must be composite as prime_factors returns list...
+    next if sum_digits($n) - sum map { sum_digits $_ } @q; ## Digit sums are equal...
+    push @sn, $n;
+    return @sn if @sn==$C;
+  }
+}
+
+
+sub smith_numbers { ## This is the short form! using &&
+  my ( $C, $n, @sn ) = (shift,3);
+  ( sum_digits( $n ) - sum map { sum_digits $_ } prime_factors( $n ) ) ||
+  ( push @sn, $n                                                     ) &&
+  ( @sn == $C                                                        ) &&
+  ( return @sn                                                       ) while $n++;
+}
+
+