use strict;
use warnings;

my $num_lights = 2;
my %lights;


#keep printing results until cancelled by user
while ( 1 ) { 
    #lights are all off
    $lights{$_} = 0 foreach (1..$num_lights);
    #flip them on and off.
    foreach my $light ( sort { $a <=> $b }(keys %lights) ){
        foreach my $divisor (2..$num_lights ) {
            if ( $light % $divisor == 0 ) { # if it divides evenly, pu
+ll the cord
                #print "$divisor divides $light evenly\n ";
                
                #this doesn't work.
                #$lights{$light} ? $lights{$light} = 0 : $lights{$ligh
+t} = 1; # turn off if it's on, and vice versa.
                
                #this works
                if ( $lights{$light} ) {
                    $lights{$light} = 0;
                } else {
                    $lights{$light} = 1;
                } 
            }
        }
    }

    #output is prettier if comment this out
    #print "on for $num_lights lights: ";
    #foreach (sort { $a <=> $b }( keys %lights ) ) {
    #        #print "$_ " if $lights{$_}; 
    #}
    #print "\n";
    
    print "off for $num_lights lights: ";
    foreach (sort { $a <=> $b }( keys %lights ) ) {
            print "$_ " unless $lights{$_}; 
    }
    print "\n";
    $num_lights++;
}
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