Check if Two Strings are Rotations of each other

check if two strings are rotations of each other” is a popular interview problem based on string data structure. Here, we are given two strings str1 and str2 and our task is to check whether these two strings are in rotation of each other or not.

Example:

INPUT:
String 1: “abcd”
String 2: “bcda”
OUTPUT:
The strings are rotation of each other
INPUT:
String 1: “abcd”
String 2: “bacd”
OUTPUT:
The strings are not in rotation of each other.

There are various methods to check if two strings are rotations of each other. Some of them are:

METHOD 1: Brute-Force Approach to check if two strings are rotations of each other

The brute-force solution of the given problem is to generate all possible rotation of first string and compare each rotation of the first string with second string. If any rotation of first string is equal to second string, then the given strings are rotation of each other. If no possible rotation of first string is equal to second string, then the given strings are not rotation of each other.The time complexity of this solution is O(n2), where ‘n’ is the length of the string.

C++ Program to check if two strings are rotations of each other is as follows:

/* C++ Program to check if two strings are rotations of each other */
#include<bits/stdc++.h>
using namespace std;
void checkStringRotation(string str1,string str2)
{
    /* Check String length */
    if(str1.length()!=str2.length())
    cout<<"Strings are not in rotation of each other\n";


    for(int i = 0 ; i< str1.length() ; i++)
    {
        char ch = str1[0];


        // Erase first character of string str1
        str1.erase(str1.begin()+0);


        // Push it back at the end of string
        str1.push_back(ch);

        /* If any rotation is equal to string2, 
           then it is rotation of each other */
        if(str1 == str2)
        {
            cout<<"Strings are in rotation of each other\n";
            return;
        }
    }
    cout<<"Strings are not in rotation of each other\n";
}
int main()
{
    string str1,str2;
    
    /* Scan strings */
    cout<<"Enter string 1:\n";
    cin>>str1;
    cout<<"Enter string 2:\n";
    cin>>str2;
    
    /* Function to check string rotation */
    checkStringRotation(str1,str2);
}

OUTPUT:
Enter string 1: 
ABBA
Enter string 2:
BBAA
Strings are in rotation of each other

METHOD 2: Efficient Method to check if two strings are rotations of each other

The efficient solution of the given problem is to concatenate first string with itself and called it as final_string. Then, search second in final_string. If second string is present in final_string as substring, then, the given strings are rotation of each other. Else, the given strings are not rotation of each other.

The time complexity of this solution is O(n^2), where ‘n’ is the length of the string.

C++ Program to check if two strings are rotations of each other is as follows:

/* C++ Program to check if two strings are rotations of each other */
#include<bits/stdc++.h>
using namespace std;
void checkStringRotation(string str1,string str2)
{
    // If the length of the string are not same,
    // The answer is false.
    
     if(str1.length()!=str2.length())
        cout<<"Strings are not in rotation of each other\n";
    // Concatenate the string with itself
    string final_string = str1 + str1;
    
    if(final_string.find(str2) != string::npos)
        cout<<"Strings are in rotation of each other\n";
    else
        cout<<"Strings are not in rotation of each other\n";
}
int main()
{
    string str1,str2;
    
    /* Scan String */
    cout<<"Enter String1:\n";
    cin>>str1;
    cout<<"Enter String2:\n";
    cin>>str2;
    /* Function to check if strings are rotation of each other */
    checkStringRotation(str1,str2);
}

OUTPUT:
Enter string 1: 
ABBA
Enter string 2:
BBAA
Strings are in rotation of each other
 

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