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Re^2: Powerset short-circuit optimization

by Limbic~Region (Chancellor)
on Oct 03, 2006 at 22:13 UTC ( #576200=note: print w/replies, xml ) Need Help??

in reply to Re: Powerset short-circuit optimization
in thread Powerset short-circuit optimization

This is the approach I previously discussed in the CB with jdporter and blokhead. The undesireable aspect is that _r() is called 29 times to yield 15 items for A,B,C,D instead of just 15. I am not sure there is a way around this but that's why I posted it.

Cheers - L~R

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Re^3: Powerset short-circuit optimization
by ikegami (Pope) on Oct 03, 2006 at 23:29 UTC

    The following only calls _v 15 times. ;) Of course, splice (or its optimized equivalent) and %seen are still called 29 times, but that's a far cry less than the possible 41. Also, even with the original code, the (presumably expensive) callback is only called 15 times.

    local *_r = sub { my @v = @_; return if not $cb->(@v); return if @v == 1; for (0..$#v) { my @v_ = @v; splice(@v_, $#v-$_, 1); _r(@v_) if not $seen{join $;, @v_}++; } };

    It breaks the rule "A,B,C should be generated before A,C", but the following might allow you to break down the problem such that your requirements can be loosened:

    my ($u_set1, $u_set2, $common) = extract_common($set1, $set2); my $psetc = powerset($common); my $pset1 = product($psetc, powerset($u_set1)); my $pset2 = product($psetc, powerset($u_set2)); my $pset = union($pset1, $pset2);

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