CS115 – Hw 1 Writing your own factorial function

Description

• f r o m m a t h i m p o r t factorial

• factorial(5)

• 120

As shown above, we can use the factorial function from the math module. Here, you’ll write your own factorial function. First, we start with a simple function that returns the product of its two inputs:

def mult(x, y):

“””Returns the product of x and y”””

return x * y

Nothing too surprising here. Now, take a look at this:

• reduce(mult, [2, 3])

6

• reduce(mult, [2, 3, 4])

24

• reduce(mult, [1, 2, 3, 4])

24

Notice that reduce takes two inputs: A function and a list and it applies that function to “compress” the list into a single value. In this case, it multiplied all of the values together.

Now, write a function factorial(n) that takes a positive integer n and returns n!.

This is “mean”…

CS115 – Hw 1

returns the sum of two numbers. You’ll need to know the number of elements in the list. This can be found using the built-in function len. For example:

• len([1, 3, 5])

3

• len(range(1,10))

9

Here is the mean function in action:

• mean([1, 2, 3])

2

• mean([1, 1, 1])

1

CS115 – Hw 1