How to rotate a string in python using string slicing

Strings are a vastly used data type to store all kinds of text data: characters, alphabets, numbers, and alphanumeric. They are immutable; therefore, we can not alter their's contents; however, we can manipulate them to achieve the desired results. Python offers various operations to manipulate strings, including concatenation, formatting, and slicing.

What is string rotation?

String rotation refers to moving the characters of a string forward or backward, making it change its index position. While rotating, we shift the position of the characters circularly. For example, if the last index character is shifted one position forward, it will occupy the first index.

There are two types of string rotation: left and right.

Left Rotation: In this case, characters from the beginning are shifted to the left and appended to the end of the string.

def rotateStr(string , num):  
    
    #slice string in start and end for left  
    leftStart = string[ num :]  
    leftEnd = string[ 0 : num ]  
    #slice string in start and end for right  
    rightStart = string[ len(string)- num :]  
    rightEnd = string[ 0 : len(string)- num]
     
    #concatenate and print the string respectively
    print 'Left Rotation : ', (leftStart + leftEnd) 
    print 'Right Rotation : ',(rightStart + rightEnd)
#Enter a number as input below
num = input()
string = 'Educative'
print('Original String : ' + string)
print('\nNumber of Rotations : {}'.format(num))
print('\nRotation is called....\n')
rotateStr(string , num)

Enter the input below

Code input area

Code explanation

Line 1: The rotateStr() function is defined that takes string and num as parameters and prints the results.
Line 4: leftStart is assigned characters from the index num till the end of the string.
Line 5: leftEnd is assigned characters from the index 0 till index num of the string.
Line 8: rightStart is assigned characters from the index len(string) - num till the end of the string.
Line 9: rightEnd is assigned characters from the index 0 till index len(string) - num of the string.
Lines 12–13: The left and right strings are concatenated and printed respectfully.
Lines 16: The input() function is used to take input for the number of rotations num to be performed on the string.
Line 17: The string is assigned text data that will be rotated.
Line 23: The rotateStr() function is called to perform the rotation operation on the given string.

String slicing using `deque`

In this method, we import the deque class from the collections module that contains a rotate() method that is directly used to perform rotation. Note that implicit string slicing occurs when the rotate() method is called.

Enter a number as input below to run the code.

#import deque class
from collections import deque
def rotateStr(string, num):
	deqStr = deque(string)
	deqStr.rotate(num)
	return ''.join(deqStr)
num = input()
string = 'Educative'
print('Original String : ' + string)
print('\nNumber of Rotations : {}'.format(num))
print('\nRotation is called....\n')
#call left and right rotations respectively
rotateLeft = rotateStr(string , -num)
rotateRight = rotateStr(string , num)
#print the rotated strings
print'Left Rotation: ', rotateLeft
print'Right Rotation: ', rotateRight

Enter the input below

Code input area

Code explanation

Line 2: The deque class is imported from collections class to use its rotate method.
Line 5: The rotateStr() function is defined that takes string and num as parameters and prints the results.
Line 6: The deqStr object is created for the deque class and is initialized with the string characters.
Line 7: The rotate() method is called from the deque class that rotates the string to the left if num is negative and to the right if num is positive.
Line 8: join() is used to join all the characters of the string together which is then returned as a result.
Line 11: The input() function is used to take input for the number of rotations num to be performed on the string.
Line 12: The string is assigned text data that will be rotated.
Line 19: rotateLeft is assigned the result received when rotateStr() function is called with a negative num parameter.
Line 20: rotateRight is assigned the result received when rotateStr() function is called with a positive num parameter.
Lines 23–24: The rotateLeft and rotateRight strings are printed respectfully.

Summary

Both methods slightly differ in functionality; however, both apply the string slicing operation to achieve the desired outputs. It is important to note that the time and space complexity for both methods is O(n); hence we can use any of them to rotate a string.

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Free Resources

How to rotate a string in python using string slicing

What is string rotation?

Simple string slicing

Code explanation

String slicing using deque

Code explanation

Summary

Test your understanding

String slicing using `deque`