sub search_idref {
    my $haystack = shift;
    my $needle = shift;
    
    my @pitchfork = sort keys %$haystack;
    my @solutions;
    
    for my $p (@pitchfork) {
        push @solutions, $p if grep 
            { $_->{'idref'} eq $needle } @{$haystack->{$p}->{'edge'}};
    }
    return @solutions;
}

print Dumper search_idref( \%s, 's241_506' );