Regular expression to find two strings anywhere in input

Question

How do I write a regular expression to match two given strings, at any position in the string?

For example, if I am searching for cat and mat

Answer 1

This is fairly easy on processing power required:

(string1(.|\n)*string2)|(string2(.|\n)*string1)

I used this in visual studio 2013 to find all files that had both string 1 and 2 in it.