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Re: Divide an array into 2 subsets to verify their sum is equal or not.

by BrowserUk (Pope)
on May 02, 2013 at 09:51 UTC ( #1031717=note: print w/ replies, xml ) Need Help??


in reply to Divide an array into 2 subsets to verify their sum is equal or not.

choroba's Explore-all-possible-combinations mechanism works okay for smallish sets (max:32 or 64 depending upon your Perl), but will get very slow for anything much larger than 20 or so.

This will very quickly (less than 0.001 of a second) find a solution, if one exists, for sets of 100s or 1000s of elements. :

#! perl -slw use strict; use Time::HiRes qw[ time ]; use List::Util qw[ sum ]; sub partition { my $sum = sum @_; return if $sum & 1; $sum /= 2; my @s = sort{ $b <=> $a } @_; my @a; my( $t, $n ) = ( 0, -1 ); $t + $s[$n] <= $sum and $t+= $s[$n] and push @a, $n while ++$n < @ +s and $t <= $sum; @a = delete @s[ @a ]; @s = grep defined, @s; return unless sum( @a ) == sum( @s ); return \@a, \@s; } our $N //= 64; my( $a, $b ) = partition 1,3,5,7; print "sum( @{ $a } ) == sum( @{ $b } )" if $a; my @set = map int( rand 100 ), 1 .. $N; my $start = time; ( $a, $b ) = partition @set; printf "Took %f seconds\n", time() - $start; if( $a ) { printf "(%u) == sum( @{ $a } ) == sum( @{ $b } )\n", sum @$a; } else { print "No solution existed for the $N element set @set"; }

A few runs:


With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.

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Re^2: Divide an array into 2 subsets to verify their sum is equal or not.
by choroba (Chancellor) on May 02, 2013 at 10:52 UTC
    It gives a wrong answer for
    2, 12, 4
    لսႽ ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ

      Corrected. Thanks.


      With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
      Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
      "Science is about questioning the status quo. Questioning authority".
      In the absence of evidence, opinion is indistinguishable from prejudice.

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