factorial – Factorial of a number – Computer Science by Example

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factorial – Factorial of a number

Write a program that computes the factorial of a number n, or simply n!.

Factorial of 0, 1, 2, 3, and 4 represented graphically.

We can recursively define the factorial of a number as:

The factorial of zero is one.
The factorial of a natural number n is the factorial of n - 1.

In symbolic terms:

0! = 1
n! = n × (n - 1)!

By the above definition, the factorial of 4 is 24

4! = 4 × 3!
4! = 4 × 3 × 2!
4! = 4 × 3 × 2 × 1!
4! = 4 × 3 × 2 × 1 × 0!
4! = 4 × 3 × 2 × 1 × 1
4! = 24.

Input and Output

Input will contain several lines with a single integer n where 0 ≤ n ≤ 12. Output should contain a line with the factorial of n.

Example input

4
6

Example output

24
720

The `factorial` function

Your program should contain a factorial function that takes an integer and returns an integer. Please refer to the information for your chosen language:

C prototype: int factorial(int n);
Haskell type: factorial :: Int -> Int
Python definition: def factorial(n):
C++ prototype: int factorial(int n);
C# definition: public static int Factorial(int x) inside a public class Program
Java definition: public static int factorial(int x) inside a public class Factorial
JavaScript definition: function factorial(x)
Lua definition: function factorial (n)
Ruby definition: def factorial(n)

Specifically for this exercise when using Python, JavaScript, Lua or Ruby, avoid using sys.exit(), process.exit(), os.exit() or exit, as your program is appended with some extra assertions in one of the test sets.

Scoring

1/6: works for the above example albeit in an incorrect format
2/6: works for the above example in the correct format
4/6: works for other examples
5/6: works for edge cases
6/6: implements the factorial function

try first: good oddeven factorial1

try next: power

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