factorial1 – Factorial of a number (easy version)

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factorial1 – Factorial of a number (easy version)

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 a single integer n where 0 ≤ n < 10. Output should contain a line with the factorial of n.

Example input 1

Example output 1

Example input 2

Example output 2

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

2/12: works for the above examples albeit in an incorrect format
4/12: works for the above examples in the correct format
8/12: works for other examples
12/12: implements the factorial function

try first: good1 signum1

try next: power1

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