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

• Last Updated : 12 Jan, 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``using` `System;`` ` `class` `GFG {``     ` `    ``/* Function checks if passed strings``    ``(str1 and str2) are rotations of``    ``each other */``    ``static` `bool` `areRotations(String str1,``                                 ``String str2)``    ``{``         ` `        ``// There lengths must be same and``        ``// str2 must be a substring of``        ``// str1 concatenated with str1. ``        ``return` `(str1.Length == str2.Length )``             ``&& ((str1 + str1).IndexOf(str2)``                                     ``!= -1);``    ``}``     ` `    ``// Driver method``    ``public` `static` `void` `Main ()``    ``{``        ``String str1 = ``"FGABCDE"``;``        ``String str2 = ``"ABCDEFG"``;`` ` `        ``if` `(areRotations(str1, str2))``            ``Console.Write(``"Strings are"``            ``+ ``" rotation s of each other"``);``        ``else``            ``Console.Write(``"Strings are "``           ``+ ``"not rotations of each other"``);``    ``}``}`` ` `// This code is contributed by nitin mittal.`

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 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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