Left Rotation and Right Rotation of a String

Difficulty Level : Medium
Last Updated : 28 Sep, 2020

Given a string of size n, write functions to perform the following operations on a string-

Left (Or anticlockwise) rotate the given string by d elements (where d <= n)
Right (Or clockwise) rotate the given string by d elements (where d <= n).

Examples:

Input : s = "GeeksforGeeks"
        d = 2
Output : Left Rotation  : "eksforGeeksGe" 
         Right Rotation : "ksGeeksforGee"  


Input : s = "qwertyu" 
        d = 2
Output : Left rotation : "ertyuqw"
         Right rotation : "yuqwert"

A Simple Solution is to use a temporary string to do rotations. For left rotation, first, copy last n-d characters, then copy first d characters in order to the temporary string. For right rotation, first, copy last d characters, then copy n-d characters.
Can we do both rotations in-place and O(n) time?
The idea is based on a reversal algorithm for rotation.

// Left rotate string s by d (Assuming d <= n)
leftRotate(s, d)
  reverse(s, 0, d-1); // Reverse substring s[0..d-1]
  reverse(s, d, n-1); // Reverse substring s[d..n-1]
  reverse(s, 0, n-1); // Reverse whole string.  

// Right rotate string s by d (Assuming d <= n)
rightRotate(s, d)

  // We can also call above reverse steps
  // with d = n-d.
  leftRotate(s, n-d)

Below is the implementation of the above steps :

C++

// C program for Left Rotation and Right
// Rotation of a String
#include<bits/stdc++.h>
using namespace std;
 
// In-place rotates s towards left by d
void leftrotate(string &s, int d)
{
    reverse(s.begin(), s.begin()+d);
    reverse(s.begin()+d, s.end());
    reverse(s.begin(), s.end());
}
 
// In-place rotates s towards right by d
void rightrotate(string &s, int d)
{
   leftrotate(s, s.length()-d);
}
 
// Driver code
int main()
{
    string str1 = "GeeksforGeeks";
    leftrotate(str1, 2);
    cout << str1 << endl;
 
    string str2 = "GeeksforGeeks";
    rightrotate(str2, 2);
    cout << str2 << endl;
    return 0;
}

Java

// Java program for Left Rotation and Right 
// Rotation of a String 
import java.util.*;
import java.io.*;
 
class GFG 
{
         
    // function that rotates s towards left by d 
    static String leftrotate(String str, int d)
    {
            String ans = str.substring(d) + str.substring(0, d);
            return ans;
    }
 
    // function that rotates s towards right by d 
    static String rightrotate(String str, int d)
    {
            return leftrotate(str, str.length() - d);
    }
 
    // Driver code
    public static void main(String args[])
    {
            String str1 = "GeeksforGeeks"; 
            System.out.println(leftrotate(str1, 2));
 
            String str2 = "GeeksforGeeks"; 
            System.out.println(rightrotate(str2, 2)); 
    }
}
 
// This code is contributed by rachana soma

Python3

# Python3 program for Left 
# Rotation and Right
# Rotation of a String
 
# In-place rotates s towards left by d
def leftrotate(s, d):
    tmp = s[d : ] + s[0 : d]
    return tmp
   
# In-place rotates s 
# towards right by d
def rightrotate(s, d):
   
   return leftrotate(s, len(s) - d)
 
# Driver code
if __name__=="__main__":
     
    str1 = "GeeksforGeeks"
    print(leftrotate(str1, 2))
  
    str2 = "GeeksforGeeks"
    print(rightrotate(str2, 2))
 
# This code is contributed by Rutvik_56

C#

// C# program for Left Rotation and Right 
// Rotation of a String 
using System; 
         
class GFG 
{
         
    // function that rotates s towards left by d 
    static String leftrotate(String str, int d)
    {
            String ans = str.Substring(d,str.Length-d) + str.Substring(0, d);
            return ans;
    }
 
    // function that rotates s towards right by d 
    static String rightrotate(String str, int d)
    {
            return leftrotate(str, str.Length - d);
    }
 
    // Driver code
    public static void Main(String []args)
    {
            String str1 = "GeeksforGeeks"; 
            Console.WriteLine(leftrotate(str1, 2));
 
            String str2 = "GeeksforGeeks"; 
            Console.WriteLine(rightrotate(str2, 2)); 
    }
}
 
/* This code is contributed by PrinciRaj1992 */

Output:

Left rotation:  eksforGeeksGe
Right rotation:  ksGeeksforGee

This article is contributed by Rishabh Jain. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
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