$"='ox'x5,$_="1 2 3\n4 5 6\n7 8 9 ";{$^=chop$";print"
$_$^ =>";{<>=~/^(\d)$/i&&s/$1/$^/m or redo}(m/^($^.){
3}|($^.{5}){2}$^|$^.{7}$^.{7}$^|^.(...$^){3}/smx|$.>8
)or redo}y/0-9/-/;print

##</code><code>##

$"='ox'x5,$_="1 2 3\n4 5 6\n7 8 9 ";{$^=chop$";print"
$_$^ =>";{<>=~/^(\d)$/i&&s/$1/$^/m or$.--&&redo}/^($^
.){3}|($^.{5}){2}$^|$^.{7}$^.{7}$^|^.(...$^){3}/smx|8
<$. or redo}y/0-9/-/;print