Given a string s1 and a string s2, write a snippet to say whether s2 is a rotation of s1 using only one call to strstr routine? (eg given s1 = ABCD and s2 = CDAB, return true, given s1 = ABCD, and s2 = ACBD , return false)

**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.  
  
**Approach1**  
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.

See also