48 lines
1.2 KiB
Plaintext
48 lines
1.2 KiB
Plaintext
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###
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### powerset_recurse0
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###
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## Chapter 5 section 4.1.1
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sub powerset_recurse ($;@) {
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my ( $set, $powerset, $keys, $values, $n, $i ) = @_;
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if ( @_ == 1 ) { # Initialize.
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my $null = { };
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$powerset = { $null, $null };
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$keys = [ keys %{ $set } ];
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$values = [ values %{ $set } ];
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$nmembers = keys %{ $set }; # This many rounds.
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$i = 0; # The current round.
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}
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# Ready?
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return $powerset if $i == $nmembers;
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# Remap.
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my @powerkeys = keys %{ $powerset };
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my @powervalues = values %{ $powerset };
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my $powern = @powerkeys;
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my $j;
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for ( $j = 0; $j < $powern; $j++ ) {
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my %subset = ( );
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# Copy the old set to the subset.
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@subset{keys %{ $powerset->{ $powerkeys [ $j ] } }} =
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values %{ $powerset->{ $powervalues[ $j ] } };
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# Add the new member to the subset.
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$subset{$keys->[ $i ]} = $values->[ $i ];
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# Add the new subset to the powerset.
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$powerset->{ \%subset } = \%subset;
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}
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# Recurse.
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powerset_recurse( $set, $powerset, $keys, $values, $nmembers, $i+1 );
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}
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