MediumProbabilitypr-398

Birthday Collision Expected Pairs

Problem

Among n people with d equally likely birthdays, the expected number of colliding pairs is C(n, 2) / d.

Given n and d, return the expected number of shared-birthday pairs.

Hint

Linearity of expectation over all pairs.

case 1

in: [23,365]

expected: 0.6931506849315069

case 2

in: [10,12]

expected: 3.75

case 3

in: [100,365]

expected: 13.561643835616438

Starter codePython

def birthday_collision_expected_pairs(n, d):
    # Your code here
    pass

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