# Java 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.```

## Java

 `// Java program to check if two given strings are rotations of ` `// each other`   `class` `StringRotation` `{` `    ``/* Function checks if passed strings (str1 and str2)` `       ``are rotations of each other */` `    ``static` `boolean` `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[] args)` `    ``{` `        ``String str1 = ``"AACD"``;` `        ``String str2 = ``"ACDA"``;`   `        ``if` `(areRotations(str1, str2))` `            ``System.out.println(``"Strings are rotations of each other"``);` `        ``else` `            ``System.out.printf(``"Strings are not rotations of each other"``);` `    ``}` `}` `// This code is contributed by  munjal `

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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