July 2, 2018

Check if a string is a rotation of another string in Python

By Mohammed Abualrob Algorithms and Data Structures, Code Snippets, Interview Questions 0 Comments

Problem

Write a Python function that checks if two strings are rotation of each other

Solution

Rotating a string means inserting a number of characters from the end of the string to the beginning of the string. Any easy trick to check if two strings are rotation of each other is to concatenate one string to itself and then check if the other string is a substring in the concatenation

Example

Take a look at the following example

S1 = "Hello"
S2 = "lloHe"
S2 + S2 = "lloHelloHE"

S1 = "Hello"

S2 = "lloHe"

S2 + S2 = "lloHelloHE"

Note that Hello is a substring in lloHelloHe

Code

Here is the code in Python

# Import python unit tests module
import unittest  

# This function returns true if the
# input strings are rotation of 
# each other
def isRotation(str1, str2):
	return len(str1) == len(str2) and str1 in str2 + str2

# This class uses python unit tests to test our code
class Tests(unittest.TestCase):    

	# Not the same length
	def test_case_01(self):                           
	    self.assertFalse(isRotation("cisco", "ciscoo"))  

	# Rotation of each other
	def test_case_02(self):
	 	self.assertTrue(isRotation("cisco", "cocis"))
	
	# Not a rotation of each other
	def test_case_03(self):                           
	    self.assertFalse(isRotation("cisco", "occis"))  
 
# Run test suite
unittest.main()

# Import python unit tests module

import unittest

# This function returns true if the

# input strings are rotation of

# each other

def isRotation(str1, str2):

return len(str1) == len(str2) and str1 in str2 + str2

# This class uses python unit tests to test our code

class Tests(unittest.TestCase):

# Not the same length

def test_case_01(self):

self.assertFalse(isRotation("cisco", "ciscoo"))

# Rotation of each other

def test_case_02(self):

self.assertTrue(isRotation("cisco", "cocis"))

# Not a rotation of each other

def test_case_03(self):

self.assertFalse(isRotation("cisco", "occis"))

# Run test suite

unittest.main()

If you run the test cases, you should get something like…

# ...
# ---------------------------------
# Ran 3 tests in 0.000s

# OK
# [Finished in 0.1s]

# ...

# ---------------------------------

# Ran 3 tests in 0.000s

# OK

# [Finished in 0.1s]

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Check if a string is a rotation of another string in Python

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