C++ Program for Minimum rotations required to get the same string

Given a string, we need to find the minimum number of rotations required to get the same string.

Examples:

Input : s = "geeks"
Output : 5

Input : s = "aaaa"
Output : 1

The idea is based on below post.
A Program to check if strings are rotations of each other or not

• Step 1: Initialize result = 0 (Here result is count of rotations
• Step 2: Take a temporary string equal to original string concatenated with itself.
• Step 3: Now take the substring of temporary string of size same as original string starting from second character (or index 1).
• Step 4: Increase the count.
• Step 5: Check whether the substring becomes equal to original string. If yes, then break the loop. Else go to step 2 and repeat it from the next index.

Below is the implementation of the above approach:

C++

// C++ program to determine minimum number
// of rotations required to yield same
// string.
#include <iostream>
using namespace std;

// Returns count of rotations to get the
// same string back.
int findRotations(string str)
{
    // tmp is the concatenated string.
    string tmp = str + str;
    int n = str.length();

    for (int i = 1; i <= n; i++) {

        // substring from i index of original
        // string size.
        string substring = tmp.substr(i, str.size());

        // if substring matches with original string
        // then we will come out of the loop.
        if (str == substring)
            return i;
    }
    return n;
}

// Driver code
int main()
{
    string str = "abc";
    cout << findRotations(str) << endl;
    return 0;
}

Output

3

Time Complexity: O(n²)
Auxiliary Space: O(n)

Please refer complete article on Minimum rotations required to get the same string for more details!