A Ruby program to compute the odds of winning an entry into the Western States Endurance Run

wser_odds.rb

#! /usr/bin/env ruby

require 'set'

COUNTS = [ 1490, 482, 207, 122].freeze # 1490 have 1 ticket, 482 have 2, etc.

N_DRAWS = 275

USER_MAP = {}

HAT, ignored = COUNTS.inject([[], 0, 0]) do |(hat, tix_index, user), n_users|
  n_users.times do
    (tix_index+1).times { hat << user }
    USER_MAP[user] = tix_index
    user += 1
  end
  [hat, tix_index + 1, user]
end

USER_MAP.freeze
HAT.freeze

N_SIMULATIONS = 10_000_000

counts = Array.new(COUNTS.size, 0)

N_SIMULATIONS.times do
  hat = HAT.sort_by { rand }
  seen = Set.new

  N_DRAWS.times do
    while seen.include?(draw = hat.pop); end
    seen << draw
    counts[USER_MAP[draw]] += 1
  end
end

percents = counts.zip(COUNTS).map do |(hits, contestants)|
  Float(hits) / contestants / N_SIMULATIONS * 100
end

require 'pp'

PP.pp(percents)