EUCLIDEAN ALGORITHM: GCD

gcd(a,b) computes the greatest common divisor of a and b
using the Euclidean algorithm.  Delete the print statement
after you have verified that gcd does what it is supposed
to do.

Example:

	>>> gcd(12345,54321)
	12345 54321 12345
	54321 12345 4941
	12345 4941 2463
	4941 2463 15
	2463 15 3
	3

Thus the gcd of 12345 and 54321 is 3.

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def gcd(a,b):
  """gcd(a,b): return greatest common divisor of a and b."""
  a, b = abs(a), abs(b)
  r = a % b
  while r > 0:
    print a, b, r    
    a, b, r = b, r, b % r
  return( b