POTD Solutions | 14 Nov'23 | Check if strings are rotations of each other or not

POTD 14 November: Check if strings are rotations of each other or not

You are given two strings of equal lengths, s1 and s2. The task is to check if s2 is a rotated version of the string s1.

Note: The characters in the strings are in lowercase.

Examples:

Input: s1 = "geeksforgeeks", s2 = "forgeeksgeeks"
Output: 1
Explanation:
s1 is geeksforgeeks, s2 is forgeeksgeeks. Clearly, s2 is a rotated version of s1 as s2 can be obtained by left-rotating s1 by 5 units.

Input: s1 = "mightandmagic", s2="andmagicmigth"
Output: 0
Explanation: Here with any amount of rotation s2 can't be obtained by s1.

Check if strings are rotations of each other or not using Strings:

The idea is to create a temp string and store the concatenation of s1 to s1 in temp, i.e temp = s1+s1. Check if s2 is a substring of temp then s1 and s2 are rotations of each other.

Illustration:

s1 = “ABACD”, s2 = “CDABA”
temp = s1.s1 = “ABACDABACD”
Since s2 is a substring of temp, s1 and s2 are rotations of each other.

Below is the implementation of the above approach:

class Solution {
public:
    // Function to check if two strings are rotations of
    // each other or not.
    bool areRotations(string s1, string s2)
    {
        // if s1 and s2 are unequal then it is not possoble
        // to get one from other by rotation.
        if (s1.length() != s2.length())
            return false;
        // concatenating s1 with s2
        string temp = s1 + s1;
        // check if s2 is substring of temp or not
        return (temp.find(s2) != string::npos);
    }
};

class Solution {
    // Function to check if two strings are rotations of
    // each other or not.
    public static boolean areRotations(String s1, String s2)
    {
        // There lengths must be same and str2 must be
        // a substring of str1 concatenated with str1.
        return (s1.length() == s2.length())
            && ((s1 + s1).indexOf(s2) != -1);
    }
}

class Solution:

    # Function to check if two strings are rotations of each other or not.
    def areRotations(self, s1, s2):
        size1 = len(s1)
        size2 = len(s2)
        temp = ''

        # Check if sizes of two strings are same
        if size1 != size2:
            return 0

        # Create a temp string with value str1.str1
        temp = s1 + s1

        # 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(s2) > 0):
            return 1
        else:
            return 0

Time Complexity: O(N), where N is the length of the string.
Auxiliary Space: O(N)