Box problem

box_problem.rb

# https://www.theguardian.com/science/2024/sep/30/did-you-solve-it-the-box-problem-that-baffled-the-boffins

def all_games
  (0...15).to_a.combination(2).map do |prize_a, prize_b|
    game(prize_a, prize_b)
  end.tally
end

def game(prize_a, prize_b)
  field = make_field(prize_a, prize_b)

  andrew_score = andrew_score(field)
  barbara_score = barbara_score(field)

  if andrew_score == barbara_score
    :tie
  elsif andrew_score < barbara_score
    :andrew
  else
    :barbara
  end
end

def make_field(prize_a, prize_b)
  field = [
    Array.new(5) { false },
    Array.new(5) { false },
    Array.new(5) { false }
  ]

  prize_a_row = prize_a / 5
  prize_a_col = prize_a % 5

  prize_b_row = prize_b / 5
  prize_b_col = prize_b % 5

  field[prize_a_row][prize_a_col] = true
  field[prize_b_row][prize_b_col] = true
  field
end

def andrew_score(field)
  (0...3).to_a.product((0...5).to_a).index do |row, col|
    field[row][col]
  end
end

def barbara_score(field)
  (0...5).to_a.product((0...3).to_a).index do |col, row|
    field[row][col]
  end
end

all_games

# {:tie=>23, :andrew=>43, :barbara=>39}