RiskProbability.rb

class RiskProbability
  @@odds = {
    [1,1] => {[1,0] => 41.67, [0,1] => 58.33},
    [2,1] => {[1,0] => 57.87, [0,1] => 42.13},
    [3,1] => {[1,0] => 65.97, [0,1] => 34.03},
    [1,2] => {[1,0] => 25.46, [0,1] => 74.54},
    [2,2] => {[2,0] => 22.76, [0,2] => 44.83, [1,1] => 32.41},
    [3,2] => {[2,0] => 37.17, [0,2] => 29.26, [1,1] => 33.58}
  }
  
  attr_reader :attackers, :defenders, :probs
  def initialize(attackers, defenders)
    @probs = Hash.new(0)
    @attackers = attackers
    @defenders = defenders
    calc_probability
  end

  def calc_probability(attackers=@attackers, defenders=@defenders, cur_prob = 1)
    if (attackers == 0 || defenders == 0)
      @probs[[attackers, defenders]] += cur_prob
    else
      cur_attackers = [attackers, 3].min
      cur_defenders = [defenders, 2].min
      outcomes = @@odds[[cur_attackers, cur_defenders]]
      outcomes.each_pair {|outcome, chance|
        calc_probability(attackers - outcome[0], defenders - outcome[1],
          cur_prob * chance/100)
      }
    end
  end
end

if (ARGV.length != 2)
  raise "Usage: ruby probs.rb <attackers> <defenders>"
end

result = RiskProbability.new(ARGV.first.to_i, ARGV.last.to_i)

result.probs.each_pair{|outcome, chance|
  puts outcome.join(",") + ": " + chance.to_s
}