hanoi

$n = 11
$towers = {}
$idx = {a: 1, b: 2, c: 3}
​
def init
  $towers = {
    a: 1.upto($n).to_a.reverse,
    b: [],
    c: []
  }
end

​init()

​def stat()
  ts = [:a, :b, :c]
  puts ts.join("\t")
  ($n - 1).downto(0).each do |i|
    [:a, :b, :c].each do |t|
      print "#{$towers[t][i]}\t"
    end
    puts
  end
end

​def m(from, to)
  d = $towers[from].pop
  dest_d = $towers[to].last
  if (to == :b && d == 1) || (dest_d && d > dest_d)
    puts("illegal move")
    exit(0)
  end
  $towers[to].push(d)
  puts "#{d} #{$idx[from]} #{$idx[to]}"
end

​

​

def move_right
  m(:a,:c)
  m(:a,:b)
  m(:c,:a)
  m(:b,:c)
  m(:a,:c)
end

​

def move_left
  m(:c,:a)
  m(:c,:b)
  m(:a,:c)
  m(:b,:a)
  m(:c,:a)
end

​

def swap()
  da = $towers[:a].last.to_i
  db = $towers[:b].last.to_i
  dc = $towers[:c].last.to_i

  ts = [da, db, dc]
  idx = [:a, :b, :c]

​  ts.each_with_index do |d, i|
    next if d == 0 || d == 1
    ts.each_with_index do |dd, ii|
      next if dd == d
​
      if dd == 0 || d < dd
        return [idx[i], idx[ii]]
      end
    end
  end
end

def done?()
  $towers[:a].last == nil && $towers[:b].last == nil
end

​
def solve
  while true
    move_right
    break if done?()
    m(*swap())
    move_left
    m(*swap())
  end
end

stat()
solve()
stat()