Permutations (nPr)

Problem

Compute the number of ways to arrange r items from n items (order matters):

P(n, r) = n! / (n-r)!

Return 0 if r < 0 or r > n.

Hint

Product of the top r terms of n!: n * (n-1) * ... * (n-r+1).

case 1

in: [5,2]

expected: 20

case 2

in: [10,3]

expected: 720

case 3

in: [5,0]

expected: 1

case 4

in: [5,5]

expected: 120

case 5

in: [3,5]

expected: 0

Starter codePython

def permutations(n, r):
    # Your code here
    pass

5 test cases · run your code against them in the editor