5 Best Ways to Check if Difference of Areas of Two Squares is Prime in Python

Rate this post

πŸ’‘ Problem Formulation: This article explores how to determine if the difference in areas of two squares is a prime number using Python. Given two squares with side lengths a and b, the task is to calculate the area difference (a^2 - b^2) and check if the result is a prime number. For example, if a = 7 and b = 4, the area difference is 33, and the desired output is to establish whether 33 is a prime number (which it is not).

Method 1: Basic Prime Checking with Area Calculation

This method incorporates a function to calculate the difference of the areas and another function to check if a number is prime. It is straightforward and easy for beginners to understand the essence of prime checking.

Here’s an example:

def is_prime(num):
    if num <= 1:
        return False
    for i in range(2, int(num ** 0.5) + 1):
        if num % i == 0:
            return False
    return True

def are_difference_prime(a, b):
    difference = a**2 - b**2
    return is_prime(difference)
  
# Example use
print(are_difference_prime(7, 4))

The output of this code snippet:

False

This code implements two functions: is_prime() checks for primality by iterating from 2 to the square root of the number and are_difference_prime() calculates the difference of the squares and uses is_prime() to return whether the difference is a prime number.

Method 2: Using the Sieve of Eratosthenes for Prime Checking

The Sieve of Eratosthenes is an ancient algorithm for finding all prime numbers up to a specified integer. It is more efficient than the basic method for multiple checks.

Here’s an example:

def sieve_of_eratosthenes(max_num):
    is_prime = [True] * (max_num + 1)
    for number in range(2, int(max_num**0.5) + 1):
        if is_prime[number]:
            for i in range(number*number, max_num + 1, number):
                is_prime[i] = False
    return is_prime

def are_difference_prime(a, b, primes):
    difference = a**2 - b**2
    return difference < len(primes) and primes[difference]

# Example use
primes = sieve_of_eratosthenes(100)
print(are_difference_prime(7, 4, primes))

The output of this code snippet:

False

This snippet uses a sieve function to generate a list indicating the primality of numbers. The are_difference_prime() function utilizes this list to quickly determine if the difference is prime, provided that the difference does not exceed the precomputed range.

Method 3: Using the SymPy Library

The third method takes advantage of the SymPy library, which comes with a built-in function for prime checking, making the code cleaner.

Here’s an example:

from sympy import isprime

def are_difference_prime(a, b):
    difference = a**2 - b**2
    return isprime(difference)

# Example use
print(are_difference_prime(7, 4))

The output of this code snippet:

False

By utilizing the isprime() function from the SymPy library, this method reduces the complexity of the code significantly. It offers a concise and high-level approach to prime checking.

Method 4: Precomputing Primes with a Function Decorator

This method involves using a decorator to precompute primes, which can be an optimization if the function is expected to check areas of multiple pairs of squares.

Here’s an example:

def memoize_primes(func):
    primes = sieve_of_eratosthenes(1000)    
    def memoized(a, b):
        return func(a, b, primes)
    return memoized

@memoize_primes
def are_difference_prime(a, b, primes):
    difference = a**2 - b**2
    return difference < len(primes) and primes[difference]

# Example use
print(are_difference_prime(7, 4))

The output of this code snippet:

False

The @memoize_primes decorator injects a precomputed list of primes into the function to check for the primality of the area difference. This improves performance when the function needs to be run multiple times.

Bonus One-Liner Method 5: Lambda with SymPy

The bonus method provides a slick one-liner using a lambda function in conjunction with the SymPy library to check if the difference of squares is prime.

Here’s an example:

from sympy import isprime

# One-liner version
are_difference_prime = lambda a, b: isprime(a**2 - b**2)

# Example use
print(are_difference_prime(7, 4))

The output of this code snippet:

False

This one-liner uses a lambda function to directly apply the isprime() function on the calculated difference. It is an elegant and concise solution that leverages the power of Python’s lambda expressions.

Summary/Discussion

  • Method 1: Basic Prime Checking. Strengths: Simple and easy to understand. Weaknesses: Not the most efficient for large numbers or multiple checks.
  • Method 2: Sieve of Eratosthenes. Strengths: Efficient for multiple prime checks within a range. Weaknesses: Memory intensive for very large ranges and initial cost of sieve computation.
  • Method 3: Using SymPy Library. Strengths: Clean and professional-looking code; handles large numbers well. Weaknesses: Depends on external library which might not be installed/enabled.
  • Method 4: Precomputing Primes with a Decorator. Strengths: Optimizes multiple checks by caching; can be a more scalable solution. Weaknesses: Increase in initial code complexity; overhead for precomputing primes.
  • Bonus Method 5: Lambda with SymPy. Strengths: Extremely concise and elegant. Weaknesses: May be less readable for beginners; requires SymPy.