Ballot Problem Probability

Problem

The ballot problem: candidate A receives a votes and candidate B receives b votes, and votes are counted in random order. Return the probability that A is strictly ahead of B throughout the count:

P = (a - b) / (a + b).

Return 0.0 when a < b or the total is 0.

Hint

The result is the reflection principle count divided by the total count.

Test cases

case 1

in: [6,4]

expected: 0.2

case 2

in: [5,3]

expected: 0.25

case 3

in: [3,3]

expected: 0

case 4

in: [4,6]

expected: 0

Starter codePython

def ballot_probability(a, b):
    # Your code here
    pass

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