input: Write a function to find the GCD of two numbers using the Euclidean algorithm. If the numbers are both zero, then return 0. If one of the numbers is zero, return the other number as the GCD. For any other pair of numbers, recursively apply the Euclidean algorithm.
  
  def findGCD(a, b):
      if b == 0:
          return a
      return findGCD(b, a % b)
  
  assert findGCD(1000, 500) == 500
  assert findGCD(8, 12) == 4
  assert findGCD(0, 0) == 0
  assert findGCD(0, 10) == 10
  assert findGCD(27, 18) == 9
output: def findGCD(a, b):
      if b == 0:
          return a
      return findGCD(b, a % b)