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.

C++

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// 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;
}

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C

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// 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;
}

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Java

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// 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 

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Python

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# 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

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C#

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// 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.

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PHP

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<?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.
?>

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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.

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