Combinations (nCr)

Problem

Compute the number of ways to choose r items from n items without regard to order:

C(n, r) = n! / (r! * (n-r)!)

Return 0 if r < 0 or r > n.

Hint

Use the multiplicative formula: product of (n-i)/(i+1) for i in [0, r).

case 1

in: [5,2]

expected: 10

case 2

in: [10,3]

expected: 120

case 3

in: [7,0]

expected: 1

case 4

in: [0,0]

expected: 1

case 5

in: [5,6]

expected: 0

Starter codePython

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

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