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# C 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? (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.```

## C

 `// C program to check if two given strings are rotations of ` `// each other` `# include ` `# include ` `# include `   `/* 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 = ``''``;` `  ``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`

Time Complexity: O(n*n), where n is the length of the string.
Auxiliary Space: O(n)

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 substring in a string of length n where length of substring is assumed to be smaller than the string. Please refer complete article on A Program to check if strings are rotations of each other or not for more details!

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