I want a regex that can match this:

It's not very useful to give a few examples of what the regex should match. /./ will match them. So will /^(Hello One World|Hello World|HelloWorld|Hello One Two World|Hello Two Three World|Hello One Three World)$/. You probably need something in between those extremes, but it's impossible to determine from your problem description where that something is. You should at least give some indication of what strings shouldn't be matched.