# C++ Program to check if strings are rotations of each other or not

• Last Updated : 23 Aug, 2022

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 ` `using` `namespace` `std;`   `/* Function checks if passed strings (str1` `   ``and str2) are rotations of each other */` `bool` `areRotations(string str1, string str2)` `{` `   ``/* Check if sizes of two strings are same */` `   ``if` `(str1.length() != str2.length())` `        ``return` `false``;`   `   ``string temp = str1 + str1; ` `  ``return` `(temp.find(str2) != string::npos);` `}`   `/* Driver program to test areRotations */` `int` `main()` `{` `   ``string str1 = ``"AACD"``, str2 = ``"ACDA"``;` `   ``if` `(areRotations(str1, str2))` `     ``printf``(``"Strings are rotations of each other"``);` `   ``else` `      ``printf``(``"Strings are not rotations of each other"``);` `   ``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) where n is the length of the new string.

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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