input: Write a function to find the largest prime factor of a given number. If the number is negative or zero, return -1.
  
  def largest_prime_factor(n):
      if n <= 0:
          return -1
  
      factors = []
      for i in range(2, int(math.sqrt(n)) + 1):
          if n % i == 0:
              factors.append(i)
              factors.append(int(n/i))
  
      prime_factors = []
      for potential_factor in factors:
          is_prime = True
          for j in range(2,int(math.sqrt(potential_factor))+1):
              if potential_factor % j == 0 and potential_factor != j: 
                  is_prime = False
          if is_prime:
              prime_factors.append(potential_factor)
  
      if prime_factors:
          return max(prime_factors)
      else:
          return n
  
  assert largest_prime_factor(331) == 331
  assert largest_prime_factor(128) == 2
  assert largest_prime_factor(63) == 7
  assert largest_prime_factor(0) == -1
  assert largest_prime_factor(-5) == -1
output: 
  def largest_prime_factor(n):
      if n <= 0:
          return -1
  
      factors = []
      for i in range(2, int(math.sqrt(n)) + 1):
          if n % i == 0:
              factors.append(i)
              factors.append(int(n/i))
  
      prime_factors = []
      for potential_factor in factors:
          is_prime = True
          for j in range(2,int(math.sqrt(potential_factor))+1):
              if potential_factor % j == 0 and potential_factor != j: 
                  is_prime = False
          if is_prime:
              prime_factors.append(potential_factor)
  
      if prime_factors:
          return max(prime_factors)
      else:
          return n
  