#!/usr/bin/perl -l
$_=pop;{print;s/.(?=(.))/$&+$1-9*($&+$1>9)/ge;chop;$_&&redo}
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#!/usr/bin/perl -l
$_=pop;{print;s/.(?=(.))/($d=$&+$1)-9*($d>9)/ge;chop;$_&&redo}
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#!/usr/bin/perl -l
$_=pop;{print;s/.(?=(.))/($d=$&+$1)>9?$d-9:$d/ge;chop;$_&&redo}
|