def problem_19_1(x, y):
    """ Write a function to swap a number in place without temporary variables. """
    # Bit-wise operations.
    #x = x ^ y
    #y = x ^ y
    #x = x ^ y
    #return (x, y)

    # Arithmetic operations.
    x = x - y
    y = y + x
    x = y - x
    return (x, y)