Syntax of strstr
const char * strstr ( const char * str1, const char * str2 );
Returns a pointer to the first occurrence of str2 in str1, or a null pointer if str2 is not part of str1.
The matching process does not include the terminating null-characters.
Append str1 to itself and do a strstr for str2. That should work.
(I am assuming strstr looks for string x within string y).
But this fails sometime...for eg. s1 = ABCDA, s2 = BCDA, s2s2 = BCDABCDA
s2s2 now contains s1, but it is not a rotation of s1.
probably other corner cases exist.
So we can improve it...by first checking whether s1 and s2 have equal number of characters or not.