POTD Solutions | 12 Nov’ 23 | Check if string is rotated by two places

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Welcome to the daily solutions of our PROBLEM OF THE DAY (POTD). We will discuss the entire problem step-by-step and work towards developing an optimized solution. This will not only help you brush up on your concepts of Strings but will also help you build up problem-solving skills.

POTD Solution 12 November 2023

POTD 12 November: Check if string is rotated by two places:

Given two strings a and b. The task is to find if the string ‘b’ can be obtained by rotating (in any direction) string ‘a’ by exactly 2 places.

Examples:

Input: string1 = amazon, string2 = azonam
Output: Yes
Explanation: amazon can be rotated anti-clockwise by two places, which will make it as azonam.

Input: string1 = geeksforgeeks, string2 = geeksgeeksfor
Output: No
Explanation: If we rotate geeksforgeeks by two place in any direction, we won’t get geeksgeeksfor.

Check if string is rotated by two places by rotating string Clockwise and Anti-clockwise:

The idea is to Rotate the String1 in both clockwise and ant-clockwise directions once. And then check if this rotated string is equal to String2.

Step-by-step approach:

• If the length of both the strings are not equal or they are less than 2, return false.
• Store anti-clockwise rotation of string by concatenating substring of size two from end to the starting of the string.
• Store clockwise rotation of string by concatenating substring of size two from beginning to the end of the string.
• Checking if any of them is equal to string, return true.

Below is the implementation of the above approach:

C++

class Solution {
public:
    // Function to check if a string can be obtained by
    // rotating another string by exactly 2 places.
    bool isRotated(string str1, string str2)
    {
        if (str1.length() != str2.length())
            return false;

        if (str1.length() <= 2 || str2.length() <= 2)
            return (str1 == str2);

        string clock_rot = "";
        string anticlock_rot = "";
        int len = str2.length();

        // storing anti-clockwise rotation of string by
        // concatenating substring of size two from end to
        // the starting of the string.
        anticlock_rot = anticlock_rot
                        + str2.substr(len - 2, 2)
                        + str2.substr(0, len - 2);

        // storing clockwise rotation of string by
        // concatenating substring of size two from beginning
        // to the end of the string.
        clock_rot = clock_rot + str2.substr(2)
                    + str2.substr(0, 2);

        // checking if any of them is equal to string, we
        // return true.
        return (str1.compare(clock_rot) == 0
                || str1.compare(anticlock_rot) == 0);
    }
};

Java

class Solution
{
    //Function to check if a string can be obtained by rotating
    //another string by exactly 2 places.
    public static boolean isRotated(String str1, String str2)
    {

        if(str1.length() <= 2 || str2.length() <= 2)
            if(str1.equals(str2)) return true;
            else return false;

        if(str1.length() != str2.length()) return false;

        int bt = 0;
        char temp,temp1;
        int flag = 0;
        char c1[] = str1.toCharArray();
        char c2[] = str2.toCharArray();
        char ck[] = new char[c1.length];
        char ak[] = new char[c1.length];

        //storing anti-clockwise rotation of string by concatenating
        //substring of size two from end to the starting of the string.
        for(int a=0; a<c1.length-2; a++){
            ck[a] = c1[a+2];
        }
        ck[c1.length-2] = c1[0];
        ck[c1.length-1] = c1[1];

        //storing clockwise rotation of string by concatenating substring
        //of size two from beginning to the end of the string.
        for(int a=2; a<c1.length; a++){
            ak[a] = c1[a-2];
        }
        ak[0] = c1[c1.length-2];
        ak[1] = c1[c1.length-1];

        //checking if any of them is equal to string, we return true.
        for(int a=0; a<c1.length; a++){
            if(ck[a]!=c2[a]&&ak[a]!=c2[a]){
                flag = 1;
                break;
            }
        }
        if(flag == 0){
            bt = 1;

        }
        flag = 0;

        if(bt == 1)
            return true;
        else
            return false;

    }

}

Python3

class Solution:

    #Function to check if a string can be obtained by rotating
    #another string by exactly 2 places.
    def isRotated(self,str1,str2):

        n=len(str2)
        if(n<3):
            return str1==str2

        #storing anti-clockwise rotation of string by concatenating
        #substring of size two from end to the starting of the string.
        anticlock_str=str2[2:]+str2[0:2]

        #storing clockwise rotation of string by concatenating substring
        #of size two from beginning to the end of the string.
        clockwise_str=str2[-2]+str2[-1]+str2[:n-2]

        #checking if any of them is equal to string, we return true.
        if(str1==anticlock_str or str1==clockwise_str):
            return True
        return False

Time Complexity: O(N), Time is taken to rotate the string and then compare the string, where N is the length of the strings.
Auxiliary Space: O(N), Space for storing clockwise and anticlockwise strings.

Check if string is rotated by two places without using Auxiliary Space:

The idea is to check directly if the string is rotated or not by comparing the two strings. 

Step-by-step approach:

• Compare for clockwise and anticlockwise rotation by using for loops and the modulo operator:
  • for clockwise direction,
    • Run a loop from i = 0 to i < N
      •  if str1[i] != str2[(i + 2) % N], then update the variable clockwise as false and break the loop.
  • For anti clockwise direction
    • Run another loop from 0 to i < N
      • if str1[i+2] % N != str2[i], then update the variable anticlockwise as false and break the loop.
• Return clockwise | anticlockwise (if any of them is true, it gives us as true result)

Below is the implementation of the above approach:

C++

class Solution {
public:
    // Function to check if a string can be obtained by
    // rotating another string by exactly 2 places.
    bool isRotated(string str1, string str2)
    {
        // Your code here
        int n = str1.length();
        bool clockwise = true, anticlockwise = true;
        for (int i = 0; i < n; i++) {
            if (str1[i] != str2[(i + 2) % n]) {
                clockwise = false; // not rotated clockwise
                break;
            }
        }

        for (int i = 0; i < n; i++) {
            if (str1[(i + 2) % n] != str2[i]) {
                anticlockwise
                    = false; // not rotated anticlockwise
                break;
            }
        }

        return clockwise
               or anticlockwise; // if any of both is true,
                                 // return true
    }
};

Java

public class Solution {
    // Function to check if a string can be obtained by
    // rotating another string by exactly 2 places.
    public boolean isRotated(String str1, String str2)
    {
        // Your code here
        int n = str1.length();
        boolean clockwise = true, anticlockwise = true;

        // Check if str2 is obtained by rotating str1
        // clockwise by 2 places
        for (int i = 0; i < n; i++) {
            if (str1.charAt(i)
                != str2.charAt((i + 2) % n)) {
                clockwise = false; // not rotated clockwise
                break;
            }
        }

        // Check if str2 is obtained by rotating str1
        // anticlockwise by 2 places
        for (int i = 0; i < n; i++) {
            if (str1.charAt((i + 2) % n)
                != str2.charAt(i)) {
                anticlockwise
                    = false; // not rotated anticlockwise
                break;
            }
        }

        // If either clockwise or anticlockwise rotation is
        // true, return true
        return clockwise || anticlockwise;
    }
}

Python3

class Solution:
    # Function to check if a string can be obtained by rotating
    # another string by exactly 2 places.
    def isRotated(self, str1: str, str2: str) -> bool:
        # Your code here
        n = len(str1)
        clockwise, anticlockwise = True, True

        # Check if str2 is obtained by rotating str1 clockwise by 2 places
        for i in range(n):
            if str1[i] != str2[(i + 2) % n]:
                clockwise = False  # not rotated clockwise
                break

        # Check if str2 is obtained by rotating str1 anticlockwise by 2 places
        for i in range(n):
            if str1[(i + 2) % n] != str2[i]:
                anticlockwise = False  # not rotated anticlockwise
                break

        # If either clockwise or anticlockwise rotation is true, return true
        return clockwise or anticlockwise

Time Complexity: O(N), Iterating over the string 2 times for comparing both the strings, where N is the length of the strings.
Auxiliary Space: O(1)