Défi de programmation Factorial

Problème

The factorial of n, written n!, is 1 × 2 × … × n. By definition 0! = 1.

Implement factorial(n).

n: A non-negative integer.

Return n!.

0 ≤ n ≤ 20, so the result fits a signed 64-bit integer.

Exemple 1

Entrée :
n = 5

Sortie attendue :
expected = 120

Entrée :
long long n = 5;

Sortie attendue :
long long expected = 120;

Entrée :
long n = 5;

Sortie attendue :
long expected = 120;

1 × 2 × 3 × 4 × 5 = 120.

Exemple 2

Entrée :
n = 0

Sortie attendue :
expected = 1

Entrée :
long long n = 0;

Sortie attendue :
long long expected = 1;

Entrée :
long n = 0;

Sortie attendue :
long expected = 1;

0! is defined as 1.