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

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.

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

C++

     
// C++ program to check if two given strings 
// are rotations of  each other 
# include <bits/stdc++.h> 
using namespace std; 
  
/* Function checks if passed strings (str1 
   and str2) are rotations of each other */
bool areRotations(string str1, string str2) 
{ 
   /* Check if sizes of two strings are same */
   if (str1.length() != str2.length()) 
        return false; 
  
   string temp = str1 + str1;  
  return (temp.find(str2) != string::npos); 
} 
  
/* Driver program to test areRotations */
int main() 
{ 
   string str1 = "AACD", str2 = "ACDA"; 
   if (areRotations(str1, str2)) 
     printf("Strings are rotations of each other"); 
   else
      printf("Strings are not rotations of each other"); 
   return 0; 
} 

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; 
} 

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  

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 

C#

// C# program to check if two given strings 
// are rotations of each other 
using System; 
  
class GFG { 
      
    /* Function checks if passed strings 
    (str1 and str2) are rotations of 
    each other */
    static bool 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 str1 = "FGABCDE"; 
        String str2 = "ABCDEFG"; 
  
        if (areRotations(str1, str2)) 
            Console.Write("Strings are"
            + " rotation s of each other"); 
        else
            Console.Write("Strings are "
           + "not rotations of each other"); 
    } 
} 
  
// This code is contributed by nitin mittal. 

PHP

<?php 
// Php program to check if  
// two given strings are  
// rotations of each other 
  
/* Function checks if passed  
strings (str1 and str2) are  
rotations of each other */
function areRotations($str1, $str2) 
{ 
/* Check if sizes of two 
   strings are same */
if (strlen($str1) != strlen($str2)) 
{ 
        return false; 
} 
  
$temp = $str1 + $str1;  
if ($temp.count($str2)> 0) 
{ 
        return true; 
} 
else
{ 
    return false; 
} 
} 
  
// Driver code 
$str1 = "AACD"; 
$str2 = "ACDA"; 
if (areRotations($str1, $str2)) 
{ 
    echo "Strings are rotations ".  
                  "of each other"; 
} 
else
{ 
    echo "Strings are not " .  
         "rotations of each other" ; 
} 
  
// This code is contributed 
// by Shivi_Aggarwal. 
?> 

Output:

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 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 substrng in a string of length n where length of substring is assumed to be smaller than the string.

My Personal Notes

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

C++

C

Java

Python

C#

PHP

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