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 program to check if two given strings are rotations of // each other # include <stdio.h> # include <string.h> # include <stdlib.h> /* 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[0] = '' ;
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;
} |
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); 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!