Random Walk Variance After n Steps

Problem

For a random walk with steps +1 with probability p and -1 otherwise, the position after n steps has variance 4 * p * (1 - p) * n. Return that variance, or 0.0 for n < 0 or p outside [0, 1].

Hint

Each step has variance 4 * p * (1 - p) and the steps are independent.

Test cases

case 1

in: [10,0.5]

expected: 10

case 2

in: [5,0.3]

expected: 4.2

case 3

in: [0,0.5]

expected: 0

case 4

in: [7,1]

expected: 0

case 5

in: [3,0.25]

expected: 2.25

Starter codePython

def random_walk_variance(n, p):
    # Your code here
    pass

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