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Re: Perl ARRAY() result

by kschwab (Vicar)
on Jan 14, 2019 at 18:44 UTC ( #1228541=note: print w/replies, xml ) Need Help??


in reply to Perl ARRAY() result

I cleaned up the code to where it can recurse in a single sub, and a few other tweaks that make it a little faster. Here's a speed comparison:

$ perl ./script
Benchmark: timing 5000 iterations of new, orig...
       new: 11 wallclock secs (10.03 u +  0.00 s = 10.03 CPU) @ 498.50/s (n=5000)
      orig: 11 wallclock secs (10.98 u +  0.00 s = 10.98 CPU) @ 455.37/s (n=5000)

And the code...see the solve2() sub for the cleaned up version.
#!/usr/bin/perl use strict; use warnings; use Benchmark qw(timethese); sub solve1 { my ( $goal, $elements ) = @_; my ( @results, $RecursiveSolve, $nextValue ); $RecursiveSolve = sub { my ( $currentGoal, $included, $index ) = @_; for ( ; $index < @$elements ; ++$index ) { $nextValue = $elements->[$index]; if ( $currentGoal > 2 * $nextValue ) { $RecursiveSolve->( $currentGoal - $nextValue, [ @$included, $nextValue ], $index + 1 ); } else { if ( $currentGoal == $nextValue ) { push @results, [ @$included, $nextValue ]; } return if $nextValue >= $currentGoal; } } }; $RecursiveSolve->( $goal, [], 0 ); undef $RecursiveSolve; #Avoid memory leak from circular referen +ce return @results; } sub solve2 { my ( $goal, $list, $index, $inc, $results ) = @_; for ( $index .. @$list - 1 ) { if ( $goal > 2 * $$list[$_] ) { solve2( $goal - $$list[$_], $list, $_ + 1, [ @$inc, $$list[$_] ], $results ); } elsif ( $$list[$_] > $goal ) { return; } elsif ( $goal == $$list[$_] ) { push @$results, [ @$inc, $$list[$_] ]; last; } } return @$results; } my $goal = 869; my $tosolve = [15,43,51,56,60,67,122,152,193,204,229,271,293,301]; timethese( 5000, { 'orig' => sub { solve1( $goal, $tosolve ) }, 'new' => sub { solve2( $goal, $tosolve, 0, [], [] ) } } ); exit; #comment out to see it produces the same result print "solve2:\n"; for ( solve2( $goal, $tosolve, 0, [], [] ) ) { print join( ',', @$_ ), "\n"; } print "solve1:\n"; for ( solve1( $goal, $tosolve ) ) { print join( ',', @$_ ), "\n"; }

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