C Program to check if strings are rotations of each other or not - GeeksforGeeks

13 Jan, 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.

C
     // 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;}
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 stringsPrototype: 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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