Function aoc::year2019::day16::binomial_mod_2

fn binomial_mod_2(n: usize, k: usize) -> usize

Computes C(n, k) % 2

This collapses to a special case of a product of only 4 possible values:

• C(0, 0) = 1
• C(1, 0) = 1
• C(1, 1) = 1
• C(0, 1) = 0

So the final value will always be one or zero. The fourth zero case happens when k has a bit not present in n so we can compute the final value using bitwise logic.