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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` `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`

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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