input: Write a function to find the GCD of two numbers. If either of the two numbers is zero, then return the other number. Otherwise, recursively find the GCD of the second number and the remainder of the first number divided by the second number.
  
  def findGCD(a, b): 
     if (b == 0): 
         return a
     return findGCD(b, a % b)
  
  assert findGCD(1000, 500) == 500
  assert findGCD(0, 500) == 500
  assert findGCD(1000, 0) == 1000
  assert findGCD(0, 0) == 0
  assert findGCD(24, 18) == 6
  assert findGCD(7, 5) == 1
output: def findGCD(a, b): 
     if (b == 0): 
         return a
     return findGCD(b, a % b)