A Program to check if strings are rotations of each other or not

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)

Algorithm: areRotations(str1, str2)

    1. Create a temp string and store concatenation of str1 to
       str1 in temp.
                          temp = str1.str1
    2. If str2 is a substring of temp then str1 and str2 are 
       rotations of each other.

    Example:                 
                     str1 = "ABACD"
                     str2 = "CDABA"

     temp = str1.str1 = "ABACDABACD"
     Since str2 is a substring of temp, str1 and str2 are 
     rotations of each other.

Implementation:

• C
• Python
• Java

// C program to check if two given strings are rotations of // each other # include <stdio.h> # include <string.h> # include <stdlib.h>   /* Function checks if passed strings (str1 and str2)    are rotations of each other */ int areRotations(char *str1, char *str2) {   int size1   = strlen(str1);   int size2   = strlen(str2);   char *temp;   void *ptr;     /* Check if sizes of two strings are same */   if (size1 != size2)      return 0;     /* Create a temp string with value str1.str1 */   temp   = (char *)malloc(sizeof(char)*(size1*2 + 1));   temp[0] = '\0';   strcat(temp, str1);   strcat(temp, str1);     /* Now check if str2 is a substring of temp */   ptr = strstr(temp, str2);     free(temp); // Free dynamically allocated memory     /* strstr returns NULL if the second string is NOT a     substring of first string */   if (ptr != NULL)     return 1;   else     return 0; }   /* Driver program to test areRotations */ int main() {     char *str1 = "AACD";     char *str2 = "ACDA";       if (areRotations(str1, str2))        printf("Strings are rotations of each other");     else        printf("Strings are not rotations of each other");       getchar();     return 0; }

Output:

Strings are rotations of each other

Library Functions Used:
strstr:
strstr finds a sub-string within a string.
Prototype: char * strstr(const char *s1, const char *s2);
See http://www.lix.polytechnique.fr/Labo/Leo.Liberti/public/computing/prog/c/C/MAN/strstr.htm for more details

strcat:
strncat concatenate two strings
Prototype: char *strcat(char *dest, const char *src);
See http://www.lix.polytechnique.fr/Labo/Leo.Liberti/public/computing/prog/c/C/MAN/strcat.htm for more details

Time Complexity: Time complexity of this problem depends on the implementation of strstr function.
If implementation of strstr is done using KMP matcher then complexity of the above program is (-)(n1 + n2) where n1 and n2 are lengths of strings. KMP matcher takes (-)(n) time to find a substrng in a string of length n where length of substring is assumed to be smaller than the string.