deal with string

[org chen]

Hi, There is an string, if each letter in the string is not belong to 
[a-z][A-Z][0-9], I want to change it to "+".
 eg. my $str = "3ijZ()a";if($str !~ /[a-z][A-Z][0-9]/){add code here}print 
$str; #output will be: 3ijZ++a please help me complete this code. Thanks
org
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