PPA-1

Question

The factorial is a positive integer \(n\) is the product of the first \(n\) positive integers.

Write a function named factorial that accepts an integer n as argument. It should return the factorial of n if n is a positive integer. It should return \(-1\) if n is a negative integer, and it should return \(1\) if n is zero.

You do not have to accept input from the user or print output to the console. You just have to write the function definition.

Hint

The main takeaway from this problem is the way functions behave when there are multiple return statements. Let us take a simpler example to begin with.

def odd_even(n):
    if n % 2 == 0:
        return 'even'
    return 'odd'

In any function that has multiple return statements, exactly one of them will be executed. The moment a return statement is executed, control exits from the function. The function odd_even given above has two return statements. When \(n\) is even, the return statement in line-3 will be executed. If \(n\) is not even, then the return statement in line-4 will be executed. Now, we come to the factorial function. This has three return statements. The body of the function is simple enough and you should be able to fill it.

Solution

def factorial(n):
    if n < 0:
        return -1
    if n == 0:
        return 1
    fact = 1
    for x in range(1, n + 1):
        fact = fact * x
    return fact

Notice the type of function. This function has a single argument and single return value.

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