Polya Contagion Update

Problem

A Polya urn starts with r red and b blue balls. After observed_reds red balls appeared in observed_total draws, return the predictive probability that the next draw is red:

P = (r + observed_reds) / (r + b + observed_total).

Return 0.0 for inconsistent or empty inputs.

Hint

Replace each drawn ball and add one of the same color, so the proportions update by counts.

Test cases

case 1

in: [1,1,1,1]

expected: 0.6666666666666666

case 2

in: [2,3,0,0]

expected: 0.4

case 3

in: [1,1,2,4]

expected: 0.5

case 4

in: [0,0,0,0]

expected: 0

Starter codePython

def polya_contagion_probability(r, b, observed_reds, observed_total):
    # Your code here
    pass

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