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.

Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready.

My Personal Notes

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

C++

C

Java

Python

C#

PHP

Recommended Posts: