Left Rotation and Right Rotation of a String
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).
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 :
Left rotation: eksforGeeksGe Right rotation: ksGeeksforGee
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