Interesting Interview Question: Check if a String is Rotated

Found an interesting interview question at Stackoverflow. How will you find a string ‘a’ is a rotated string of some string ‘b’ (say, or some other reference string, but known)? Example: a= ‘stackoverflow’, b = ‘overflowstack’, then ‘a’ is rotated string of ‘b’. a= ‘stackoverflow’, b= ‘flowrevostack’, then ‘a’ is NOT rotated string of ‘b’. [...]