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Left Rotation and Right Rotation of a String

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  • Difficulty Level : Medium
  • Last Updated : 29 Jun, 2022

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

  1. Left (Or anticlockwise) rotate the given string by d elements (where d <= n)
  2. 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"

Method#1: 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 */

Javascript




<script>
 
// JavaScript program for Left Rotation and Right
// Rotation of a String
 
// Function that rotates s towards left by d
function leftrotate(str, d)
{
    var ans = str.substring(d, str.length) +
              str.substring(0, d);
    return ans;
}
 
// Function that rotates s towards right by d
function rightrotate(str, d)
{
    return leftrotate(str, str.length - d);
}
 
// Driver code
var str1 = "GeeksforGeeks";
document.write(leftrotate(str1, 2) + "<br>");
 
var str2 = "GeeksforGeeks";
document.write(rightrotate(str2, 2) + "<br>");
 
// This code is contributed by rdtank
 
</script>

Output

eksforGeeksGe
ksGeeksforGee

               

Time Complexity: O(N), where N is the size of the given string.

Auxiliary Space: O(1), no extra space is required, so it is a constant.

Method#2: We can use extended string which is double in size of normal string to rotate string. For left rotation, access the extended string from index n to the index len(string) + n. For right rotation, rotate the string left with size-d places. 

The idea is 

// Left rotate string s by d 
leftRotate(s, n)
  temp = s + s; // extended string 
  l1  = s.length // length of string 
  return temp[n : l1+n] //return rotated string.  

// Right rotate string s by n
rightRotate(s, n)
  // We can also call above reverse steps
  // with x = s.length - n.
  leftRotate(s, x-n)

Below is implementation of above approach

C++




// C++ program for Left Rotation and Right
// Rotation of a String
#include <bits/stdc++.h>
using namespace std;
 
// Rotating the string using extended string
string leftrotate(string str1, int n)
{
 
    // creating extended string and index for new rotated
    // string
    string temp = str1 + str1;
    int l1 = str1.size();
 
    string Lfirst = temp.substr(n, l1);
 
    //      now returning  string
    return Lfirst;
}
// Rotating the string using extended string
string rightrotate(string str1, int n)
{
 
    return leftrotate(str1, str1.size() - n);
}
 
// Driver code
int main()
{
    string str1 = leftrotate("GeeksforGeeks", 2);
    cout << str1 << endl;
 
    string str2 = rightrotate("GeeksforGeeks", 2);
    cout << str2 << endl;
    return 0;
}

Java




// Java program for Left Rotation and Right
// Rotation of a String
import java.io.*;
import java.util.*;
 
class GFG {
 
  // Rotating the string using extended string
  static String leftrotate(String str1, int n)
  {
 
    // creating extended string and index for new
    // rotated string
    String temp = str1 + str1;
    int l1 = str1.length();
 
    String Lfirst = temp.substring(n, n + l1);
 
    // now returning  string
    return Lfirst;
  }
 
  // Rotating the string using extended string
  static String rightrotate(String str1, int n)
  {
    return leftrotate(str1, str1.length() - n);
  }
 
  // 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 Abhijeet Kumar(abhijeet19403)

Python3




# Python3 program for Left
# Rotation and Right
# Rotation of a String
 
def leftrotate(str1, n):
    # extended string
    temp = str1 + str1
    l = len(str1)
    # Return string
    return temp[n :l+n]
def rightrotate(str1, n):
    return leftrotate(str1, len(str1)-n)
     
    return temp[l-n : l1-n  ]
# Driver code
if __name__=="__main__":
     
    str1 = "GeeksforGeeks"
    print(leftrotate(str1, 2))
 
    str2 = "GeeksforGeeks"
    print(rightrotate(str2, 2))
 
# This code is contributed by sam snehil

C#




// C# program for Left Rotation and Right
// Rotation of a String
using System;
 
class GFG {
 
    // Rotating the string using extended string
    static String leftrotate(String str1, int n)
    {
 
        // creating extended string and index for new
        // rotated string
        String temp = str1 + str1;
        int l1 = str1.Length;
 
        String Lfirst = temp.Substring(n, l1);
 
        // now returning  string
        return Lfirst;
    }
 
    // Rotating the string using extended string
    static String rightrotate(String str1, int n)
    {
        return leftrotate(str1, str1.Length - n);
    }
 
    // 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 Abhijeet Kumar(abhijeet19403)

Javascript




// JavaScript program for Left Rotation and Right
// Rotation of a String
 
// Function that rotates string towards left by n
function leftrotate(str1, n)
{
    var temp = str1 + str1;
    var l1 = str1.length;
     
    var Lfirst = temp.substr(n,l1);
 
//      now returning  string
    return Lfirst;
}
 
// Function that rotates string towards right by n
function rightrotate(str, d)
{
    return leftrotate(str, str.length - d);
}
 
// Driver code
var str1 = "GeeksforGeeks";
console.log(leftrotate(str1, 2));
 
var str2 = "GeeksforGeeks";
console.log(rightrotate(str2, 2) );
 
// This code is contributed by sam snehil

Output

eksforGeeksGe
ksGeeksforGee

Time Complexity: O(N), where N is the size of the given string.

Auxiliary Space: O(n), where N is the size of the given string.

This article is contributed by Aart_Rathi and Rishabh Jain. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
 


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