Java Program for Left Rotation and Right Rotation of a String

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"

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 : 

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

Output:

Left rotation:  eksforGeeksGe
Right rotation:  ksGeeksforGee                 

Time Complexity: O(N), as we are using a loop to traverse N times so it will cost us O(N) time.
Auxiliary Space: O(1), as we are not using any extra space.

Please refer complete article on Left Rotation and Right Rotation of a String for more details!