brute force towers of hanoi

hanoi.rb

towers = [[nil,4,3,2,1],[nil],[nil]]
valid  = [[nil],[nil],[nil,4,3,2,1]]

moves  = []

record = ->(disc, from, to) {
  names = { 0 => 'left  ', 1 => 'center', 2 => 'right ' }
  moves << "disc %s: %s -> %s" % [disc, names[from], names[to]]
}

move = ->(towers) {
  return if towers == valid
  disc       = towers.select(&:last).sample.last
  from_tower = towers.find { |t| t.last == disc }
  from       = towers.index(from_tower)
  to_tower   = towers.select { |t| t.last.nil? || t.last > disc }.sample
  to         = towers.index(to_tower)

  if to
    towers[to].push towers[from].pop
    record[disc, from, to]
  end
  move[towers]
}

move[towers]

puts moves
puts "Finished in #{moves.count}"