String slicing in Python to rotate a string
Given a string of size n, write functions to perform following operations on 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"Method 1: We have existing solution for this problem please refer Left Rotation and Right Rotation of a String link. We will solve this problem quickly in python using String Slicing. Approach is very simple,
- Separate string in two parts first & second, for Left rotation Lfirst = str[0 : d] and Lsecond = str[d :]. For Right rotation Rfirst = str[0 : len(str)-d] and Rsecond = str[len(str)-d : ].
- Now concatenate these two parts second + first accordingly.
Implementation:
Python3
# Function to rotate string left and right by d lengthdef rotate(input,d): # slice string in two parts for left and right Lfirst = input[0 : d] Lsecond = input[d :] Rfirst = input[0 : len(input)-d] Rsecond = input[len(input)-d : ] # now concatenate two parts together print ("Left Rotation : ", (Lsecond + Lfirst) ) print ("Right Rotation : ", (Rsecond + Rfirst))# Driver programif __name__ == "__main__": input = 'GeeksforGeeks' d=2 rotate(input,d) |
Output:
Left Rotation : eksforGeeksGe Right Rotation : ksGeeksforGee
Method 2: We use extended string to rotate the string. We will solve this problem quickly in python by slicing extended string. Approach is very simple,
Use extended string Extend_str, for Left rotation Lfirst = Extended_str[n : l1+n] . For Right rotation Rfirst = str[l1-n : l2-n].
Now print this string.
Implementation:
Python3
# Function to rotate string left and right by d lengthdef rotate(str1,n): # Create the extended string and index of for rotation temp = str1 + str1 l1 = len(str1) l2 = len(temp) Lfirst = temp[n : l1+n] Lfirst = temp[l1-n : l2-n] # now printing the string print ("Left Rotation : ", Lfirst) print ("Right Rotation : ", Lfirst )# Driver programif __name__ == "__main__": input = 'GeeksforGeeks' d=2 rotate(input,d) |
Left Rotation : ksGeeksforGee Right Rotation : ksGeeksforGee
Approach#3: Using deque
Take the input string s and the number of rotations d. Create a deque from the string s. Rotate the deque by d positions to the left or right using the rotate() method. Convert the deque back to a string using join() method and return the rotated string.
Algorithm
1. Take the input string s and the number of rotations d.
2. Create a deque from the string s.
3. If d is positive, rotate the deque to the left by d positions using the rotate() method.
If d is negative, rotate the deque to the right by -d positions using the rotate() method.
4. Convert the deque back to a string using join() method and return the rotated string.
Python3
from collections import dequedef rotate_string(s, d): deq = deque(s) if d > 0: deq.rotate(-d) else: deq.rotate(abs(d)) return ''.join(deq)s = 'GeeksforGeeks'd = 2left_rotated = rotate_string(s, d)right_rotated = rotate_string(s, -d)print("Left Rotation: ", left_rotated)print("Right Rotation: ", right_rotated) |
Left Rotation: eksforGeeksGe Right Rotation: ksGeeksforGee
Time complexity: O(n), where n is the length of the string s.
Auxiliary Space: O(n), where n is the length of the string s.
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