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
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);
strcat:
strncat concatenate two strings
Prototype: char *strcat(char *dest, const char *src);
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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