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

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  • 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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