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Minimum rotations required to get the same string

  • Difficulty Level : Medium
  • Last Updated : 04 Oct, 2021

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

 

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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 equals 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. 
 
 



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;
}

Java




// Java program to determine minimum number
// of rotations required to yield same
// string.
 
import java.util.*;
 
class GFG
{
    // Returns count of rotations to get the
    // same string back.
    static 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.substring(
                      i, i+str.length());
     
            // if substring matches with original string
            // then we will come out of the loop.
            if (str.equals(substring))
                return i;
        }
        return n;
    }
 
    // Driver Method
    public static void main(String[] args)
    {
            String str = "aaaa";
        System.out.println(findRotations(str));
    }
}
/* This code is contributed by Mr. Somesh Awasthi */

Python3




# Python 3 program to determine minimum
# number of rotations required to yield
# same string.
 
# Returns count of rotations to get the
# same string back.
def findRotations(str):
     
    # tmp is the concatenated string.
    tmp = str + str
    n = len(str)
 
    for i in range(1, n + 1):
         
        # substring from i index of
        # original string size.
        substring = tmp[i: i+n]
 
        # if substring matches with
        # original string then we will
        # come out of the loop.
        if (str == substring):
            return i
    return n
 
# Driver code
if __name__ == '__main__':
 
    str = "abc"
    print(findRotations(str))
 
# This code is contributed
# by 29AjayKumar.

C#




// C# program to determine minimum number
// of rotations required to yield same
// string.
using System;
 
class GFG {
     
    // Returns count of rotations to get
    // the same string back.
    static 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.Substring(i, str.Length);
     
            // if substring matches with
            // original string then we will
            // come out of the loop.
            if (str == substring)
                return i;
        }
         
        return n;
    }
 
    // Driver Method
    public static void Main()
    {
        String str = "abc";
         
        Console.Write(findRotations(str));
    }
}
 
// This code is contributed by nitin mittal.

PHP




<?php
// PHP program to determine minimum
// number of rotations required to
// yield same string.
 
// Returns count of rotations
// to get the same string back.
function findRotations($str)
{
    // tmp is the concatenated string.
    $tmp = ($str + $str);
    $n = strlen($str);
 
    for ( $i = 1; $i <= $n; $i++)
    {
 
        // substring from i index
        // of original string size.
        $substring = $tmp.substr($i,
                          strlen($str));
 
        // if substring matches with
        // original string then we will
        // come out of the loop.
        if ($str == $substring)
            return $i;
    }
    return $n;
}
 
// Driver code
$str = "abc";
echo findRotations($str), "\n";
 
// This code is contributed
// by Sachin
?>

Javascript




<script>
// javascript program to determine minimum number
// of rotations required to yield same
// string.
 
    // Returns count of rotations to get the
    // same string back.
    function findRotations( str) {
        // tmp is the concatenated string.
        var tmp = str + str;
        var n = str.length;
 
        for (var i = 1; i <= n; i++) {
 
            // substring from i index of original
            // string size.
 
            var substring = tmp.substring(i ,str.length);
 
            // if substring matches with original string
            // then we will come out of the loop.
            if (str===(substring))
                return i;
        }
        return n;
    }
 
    // Driver Method
     
        var str = "abc";
        document.write(findRotations(str));
 
// This code contributed by gauravrajput1
</script>

Output: 
 

3

Time Complexity: O(n2
Alternate Implementation in Python : 
 

Python3




# Python 3 program to determine minimum
# number of rotations required to yield
# same string.
  
# input
string = 'aaaa'
check = ''
  
for r in range(1, len(string)+1):
  # checking the input after each rotation
  check = string[r:] + string[:r]
    
  # following if statement checks if input is
  # equals to check , if yes it will print r and
  # break out of the loop
  if check == string:
    print(r)
    break
  
# This code is contributed
# by nagasowmyanarayanan.

Output: 
 

1

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Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
 




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