Turns out, hints from others, we don't need to loop through every possible pairings permutation. Just need to sort the input numbers and sum up every evenly indexed (0-indexed array) number.

1 files changed, 5 insertions, 31 deletions

diff --git a/challenge-206/kjetillll/perl/ch-2.pl b/challenge-206/kjetillll/perl/ch-2.pl
index 0ec1e5e59e..96afc91618 100644
--- a/challenge-206/kjetillll/perl/ch-2.pl
+++ b/challenge-206/kjetillll/perl/ch-2.pl
@@ -1,37 +1,11 @@
 #!/usr/bin/perl
-use warnings; use strict;
-#use Acme::Tools;
+use warnings; use strict; use List::Util 'sum';
 
-my @array = @ARGV;                #input from command line args
-@array = (1,2,3,4) if not @array; #...or use test case
+my @array = @ARGV;                 #use input from command line args
+@array = (1,2,3,4) if not @array;  #...or use test case
 #@array = (0,2,1,3) if not @array; #...or use test case
 
 print "Input: @array\n";
-print "Max sum: ", maxsum(@array), "\n";
+print "Max sum: ", maxminsum(@array), "\n";
 
-
-sub maxsum {
-    my $max;
-    for my $perm_array ( perm(@_) ){
-	my $sum;
-	while(@$perm_array){  #loop the pairs ($a,$b) of current permutation
-	    my($a,$b) = splice@$perm_array,0,2;
-	    $sum += $a<$b ? $a : $b;
-	}
-	$max = $sum if !defined$max or $sum>$max;
-    }
-    $max
-}
-
-sub perm {
-  my(@i,@r) = 0..$#_;
-  @_ || return;
-  while ( push @r, [@_[@i]] ) {
-    my $p = $#i || last;
-    --$p || last while $i[$p-1] > $i[$p];
-    push @i, reverse splice @i, my$q=$p;
-    ++$q while $i[$p-1] > $i[$q];
-    @i[$p-1,$q] = @i[$q,$p-1];
-  }
-  @r
-}
+sub maxminsum { sum( (sort{$a<=>$b}@_)[map 2*$_,0..$#_/2] ) }