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String slicing in Python to Rotate a String

Last Updated : 30 Jun, 2023
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Given a string of size n, write functions to perform following operations on 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"

Rotate string for string slicing

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,

  1. 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 : ].
  2. Now concatenate these two parts second + first accordingly.

Implementation:

Python3




# Function to rotate string left and right by d length
 
def 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 program
if __name__ == "__main__":
    input = 'GeeksforGeeks'
    d=2
    rotate(input,d)


Output:

Left Rotation  : eksforGeeksGe 
Right Rotation : ksGeeksforGee

Using extending the string

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 length
 
def 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 program
if __name__ == "__main__":
    input = 'GeeksforGeeks'
    d=2
    rotate(input,d)


Output

Left Rotation :  ksGeeksforGee
Right Rotation :  ksGeeksforGee

String slicing in Python to Rotate a String 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 deque
 
def rotate_string(s, d):
    deq = deque(s)
    if d > 0:
        deq.rotate(-d)
    else:
        deq.rotate(abs(d))
    return ''.join(deq)
 
s = 'GeeksforGeeks'
d = 2
 
left_rotated = rotate_string(s, d)
right_rotated = rotate_string(s, -d)
 
print("Left Rotation: ", left_rotated)
print("Right Rotation: ", right_rotated)


Output

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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