5 Best Ways to Check If a String Can Be Obtained by Rotating Another String 2 Places in Python

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πŸ’‘ Problem Formulation: You may encounter situations in coding where you need to determine if a string can be considered a rotated version of another string by exactly two places. This can be especially relevant in data analysis, cryptography, and pattern recognition tasks. For instance, if we take the string “Pythonics”, a two-place rotation would give us “onicsPyth”. The goal is to detect if such a transformation is possible between two given strings.

Method 1: Using String Slicing

This method involves moving the initial two characters of the string to the end or bringing the last two characters to the beginning. String slicing in Python is a highly efficient way to carry out this operation and can be used to easily compare the altered string with another to check for rotation equivalence.

Here’s an example:

def is_rotated(str1, str2):
    if len(str1) != len(str2):
        return False
    return str1 == str2[2:] + str2[:2] or str1 == str2[-2:] + str2[:-2]

print(is_rotated("Pythonics", "onicsPyth"))  # This should return True

Output: True

This code defines a function is_rotated() that takes two strings and first checks if their lengths are not equal, it returns False. Then it compares the original string with the rotated versions of the second string by slicing it. It will return True if a match is found, suggesting a rotation is possible.

Method 2: Using List Conversion and Concatenation

This technique converts strings to lists to perform the rotation directly on the lists, reconverting them back to strings for comparison. This method handles mutability more explicitly and is useful when working with languages that do not support direct string slicing.

Here’s an example:

def is_rotated_list(str1, str2):
    if len(str1) != len(str2):
        return False
    list_str2 = list(str2)
    return str1 == ''.join(list_str2[2:] + list_str2[:2]) or str1 == ''.join(list_str2[-2:] + list_str2[:-2])

print(is_rotated_list("Pythonics", "onicsPyth"))  # This should return True

Output: True

The function is_rotated_list() follows the same logic as Method 1 but uses list conversion for the rotation process. The function converts the second string str2 into a list to perform the rotation and then converts it back to a string for comparison.

Method 3: Using the in-built rotate method from collections

The collections module in Python offers a deque data type that supports a rotate operation. We can leverage this functionality to make our code more expressive and avoid manual list operations.

Here’s an example:

from collections import deque

def is_rotated_deque(str1, str2):
    if len(str1) != len(str2):
        return False
    d = deque(str2)
    d.rotate(2)
    return ''.join(d) == str1 or ''.join(reversed(d)) == str1

print(is_rotated_deque("Pythonics", "onicsPyth"))  # This should return True

Output: True

The is_rotated_deque() function creates a deque object from the second string, then applies the rotate() method to perform rotation. The result is cast back to a string and compared with the first string. If they match, it implies a rotation is possible.

Method 4: Using Regular Expressions

Regular expressions can be used to detect patterns of rotation. This method is versatile and can be extended for more complex rotation detection cases.

Here’s an example:

import re

def is_rotated_regex(str1, str2):
    if len(str1) != len(str2):
        return False
    pattern = '(?:(.{' + str(len(str1)-2) + '})(.{2}))'
    matches = re.match(pattern, str2)
    return matches and (str1 == matches[2] + matches[1] or str1 == str2)

print(is_rotated_regex("Pythonics", "onicsPyth"))  # This should return True

Output: True

By using regular expressions in the is_rotated_regex() function, we extract the two parts of the second string and flip them to compare them with the first string. The function builds a dynamic pattern based on the length of the input strings and checks for rotation.

Bonus One-Liner Method 5: Using String Concatenation

A creative one-liner approach can also solve this problem. By doubling the second string and searching for the first string inside it, we can deduce the rotational relationship in a simple and elegant way.

Here’s an example:

is_rotated_one_liner = lambda x, y: len(x) == len(y) and (x in (y * 2)[2:] or x in (y * 2)[:-2])
print(is_rotated_one_liner("Pythonics", "onicsPyth"))  # This should return True

Output: True

Here, is_rotated_one_liner() is a lambda function that checks whether the first string is a substring of the doubled second string minus the initial or final two characters, thus checking for two-place rotation.

Summary/Discussion

  • Method 1: String Slicing. It is direct and highly efficient in Python. However, not applicable if mutability is required.
  • Method 2: List Conversion and Concatenation. Handles mutability, but slightly more verbose and indirect in comparison to string slicing.
  • Method 3: Using deque. More idiomatic and expressive. However, introduces additional overhead from importing the collections module.
  • Method 4: Regular Expressions. Flexible and powerful for more complex patterns, but overkill for simple rotations and requires understanding regex.
  • Bonus Method 5: One-Liner String Concatenation. Simple and clever for those familiar with Pythonic idioms, but may be less readable for beginners.