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A Program to check if strings are rotations of each other or not
• Difficulty Level : Easy
• Last Updated : 06 Nov, 2020

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;``}`

## 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;``}`

## 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 `

## Python

 `    ` `# Python program to check if strings are rotations of``# each other or not`` ` `# Function checks if passed strings (str1 and str2)``# are rotations of each other``def` `areRotations(string1, string2):``    ``size1 ``=` `len``(string1)``    ``size2 ``=` `len``(string2)``    ``temp ``=` `''`` ` `    ``# Check if sizes of two strings are same``    ``if` `size1 !``=` `size2:``        ``return` `0`` ` `    ``# Create a temp string with value str1.str1``    ``temp ``=` `string1 ``+` `string1`` ` `    ``# Now check if str2 is a substring of temp``    ``# string.count returns the number of occurrences of``    ``# the second string in temp``    ``if` `(temp.count(string2)> ``0``):``        ``return` `1``    ``else``:``        ``return` `0`` ` `# Driver program to test the above function``string1 ``=` `"AACD"``string2 ``=` `"ACDA"`` ` `if` `areRotations(string1, string2):``    ``print` `"Strings are rotations of each other"``else``:``    ``print` `"Strings are not rotations of each other"`` ` `# This code is contributed by Bhavya Jain`

## 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.`

## PHP

 ` 0)``{``        ``return` `true;``}``else``{``    ``return` `false;``}``}`` ` `// Driver code``\$str1` `= ``"AACD"``;``\$str2` `= ``"ACDA"``;``if` `(areRotations(``\$str1``, ``\$str2``))``{``    ``echo` `"Strings are rotations "``. ``                  ``"of each other"``;``}``else``{``    ``echo` `"Strings are not "` `. ``         ``"rotations of each other"` `;``}`` ` `// This code is contributed``// by Shivi_Aggarwal.``?>`

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 substrng in a string of length n where length of substring is assumed to be smaller than the string.

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