Write a recursive method named factorial that accepts an integer n as a parameter and returns the factorial of n, or n!. A factorial of an integer is defined as the product of all integers from 1 through that integer inclusive. For example, the call of factorial(4) should return 1 * 2 * 3 * 4, or 24. The factorial of 0 and 1 are defined to be 1. You may assume that the value passed is non-negative and that its factorial can fit in the range of type int. Do not use loops or auxiliary data structures; solve the problem recursively.