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sub wgc {
    return if $seen{"@_"}++;
...
}

wgc

bg
g
...
bcw
cw
bcgw

sub w{return if$s{"@_"}++;my%x=@_;if($x{b}&$x{c}&$x{g}&$x{w}){print+(s
+ort keys%$_),"\n"for@h;exit;}elsif(($x{b}||!($x{c}&&$x{g}||$x{g}&&$x{
+w}))&&(!$x{b}||!(!$x{c}&&!$x{g}||!$x{g}&&!$x{w}))){if($x{b}){delete$x
+{b};for(A,keys%x){my%y=%x;delete$y{$_};local@h=(@h,\%y);w(%y)}}else{$
+x{b}=1;{local@h=(@h,\%x);w(%x);}for(qw(c g w)){if(!$x{$_}){my%y=(%x,$
+_,1);local@h=(@h,\%y);w(%y)}}}}}w