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sub nn_single {
    @_=sort{$a<=>$b}@_;
    $_{abs$_[$_]-$_[$_-1]}=[$_-1,$_]for 1..$#_;
    @_[@{$_{(sort{$a<=>$b}keys%_)[0]}}]
}

sub nn_dup {
    my$s=sub{sort{$a<=>$b}keys%_};
    @_{@_}=0;
...
    $_{abs$_[$_]-$_[$_-1]}=[$_-1,$_]for 1..$#_;
    @_[@{$_{(&$s)[0]}}]
}