sub f {
($a=shift)=~s/_/[^$a]/g;grep/^$a$/i,@{$_[0]}
#23456789_123456789_123456789_123456789_1234
}

##</code><code>##

sub g {
shift;for(@{+shift}){s/[@_]//g;$c{$_}++for split//}(sort{$c{$b}<=>$c{$a}}%c)[0]
#23456789_123456789_123456789_123456789_123456789_123456789_123456789_123456789
}

##</code><code>##

sub g {
shift;for(@{+shift}){s/[@_]//g;$b||=chop}$b
#23456789_123456789_123456789_123456789_123
}