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

• Last Updated : 13 Jun, 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.```

## 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`

Output:

`Strings are rotations of each other`

Time Complexity : O(n)

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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