The factorial of a whole number n, written n!, is the product of all the whole numbers from 1 up to n. For example 5! = 1 * 2 * 3 * 4 * 5 = 120. By definition, 0! = 1.
Write a function factorial(n) that returns n!. Use a loop rather than a library function.
Examples
Input: n = 5
Output: 120
Input: n = 0
Output: 1
Constraints
0 <= n <= 15
Goals
- Loop over a sequence of numbers with for and range()
- Know that range(a, b) stops just before b
- Build up a result step by step in an accumulator variable