5 Best Ways to Check if Concatenation of Two Strings is Balanced in Python

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πŸ’‘ Problem Formulation: We are often faced with the challenge of verifying if the concatenation of two strings results in a “balanced” string. A balanced string is one where the count of each unique character is the same. For instance, if string A = "xx" and string B = "yy", their concatenation A+B = "xxyy" is balanced since both ‘x’ and ‘y’ occur twice.

Method 1: Using Counter from collections

This method involves utilizing the Counter class from the collections module to count the occurrence of each character in the concatenated string, and then checking if all counts are equal. It provides a direct and readable approach to solve the problem.

Here’s an example:

from collections import Counter

def is_balanced(str1, str2):
    count = Counter(str1 + str2)
    return all(value == list(count.values())[0] for value in count.values())

# Example usage
print(is_balanced("aabb", "bbaa"))

Output: True

Here, we defined a function is_balanced() that takes two strings, concatenates them, and counts character occurrences with Counter. It then checks if all values in the counter are the same, indicating a balanced string. If they are, it returns True; otherwise, False.

Method 2: Using defaultdict

Combining defaultdict from the collections module with a simple loop can give us a tally of characters which can be compared for balance. This method works well with large strings and is also easy to understand.

Here’s an example:

from collections import defaultdict

def is_balanced(str1, str2):
    char_tally = defaultdict(int)
    for char in str1 + str2:
        char_tally[char] += 1
    return len(set(char_tally.values())) == 1

# Example usage
print(is_balanced("xxyz", "yyzz"))

Output: True

Function is_balanced() loops over each character in the concatenated string, incrementing its count in a defaultdict. After tallying, it ensures all counts are identical. This is done by converting the counts to a set and verifying that this set contains only one element (implying all counts are equal).

Method 3: Using Regular Expressions

This method makes use of Python’s regular expressions library, re, to find all non-overlapping occurrences of characters and then checks if their counts are equal. This method might be slower but can be preferable for pattern-based string analysis.

Here’s an example:

import re
from collections import defaultdict

def is_balanced(str1, str2):
    joined_str = str1 + str2
    char_tally = defaultdict(int)
    for char in set(joined_str):
        char_tally[char] = len(re.findall(char, joined_str))
    return len(set(char_tally.values())) == 1

# Example usage
print(is_balanced("abc", "cba"))

Output: True

By initially concatenating the strings, we search for each unique character using re.findall() and count their occurrences. Then we verify these counts are equal to determine if the combined string is balanced.

Method 4: Using lambda and map

This concise method defines a lambda function to check if all elements in an iterable are equal and uses map() to apply a function to each character in the set of concatenated strings. It showcases the power of functional programming paradigms.

Here’s an example:

def is_balanced(str1, str2):
    all_equal = lambda x: len(set(x)) == 1
    count_map = map(str1.count, set(str1 + str2))
    return all_equal(count_map)

# Example usage
print(is_balanced("xy", "yx"))

Output: True

By creating an all_equal lambda function, we ensure all counted characters have the same number of occurrences. The map() function counts each character’s occurrences and passes a list of these counts to all_equal.

Bonus One-Liner Method 5: Pythonic Approach with List Comprehension

This method uses Python list comprehensions to count character occurrences from the concatenated string and checks if they’re equal in one line. It’s a very Pythonic and elegant solution.

Here’s an example:

is_balanced = lambda s1, s2: len(set([s1.count(i) for i in set(s1+s2)])) == 1

# Example usage
print(is_balanced("test", "tset"))

Output: True

The lambda function uses set and list comprehension. It counts occurrences of each character in the concatenated string and makes sure that converting them to a set results in only one unique count.

Summary/Discussion

  • Method 1: Using Counter from collections. Efficient and easy to read. Well suited for large datasets. However, it is an additional import statement in your code.
  • Method 2: Using defaultdict. Versatile and simple. It provides immediate access to character tallies. Might be slightly less efficient for small strings compared to Counter.
  • Method 3: Using Regular Expressions. Powerful for pattern matching but slower than other methods. Not recommended for simple counting tasks.
  • Method 4: Using lambda and map. Shows the beauty of functional programming paradigms. It’s concise but might be less intuitive for people not familiar with functional concepts.
  • Bonus Method 5: Pythonic Approach with List Comprehension. It’s a one-liner that’s elegant and straightforward. However, it has the potential to be less efficient because of multiple counts on the same characters for large strings.