http://icpc2010.honiden.nii.ac.jp/domestic-contest/problems#section_D

gistfile1.rb

require 'pp'

def neighbor(s)
  [[s[0],s[1]-1],
   [s[0],s[1]+1],
   [s[0]+1,s[1]],
   [s[0]-1,s[1]]]
end

def upper(s)
  [s[0]+1,s[1]]  
end

def lower(s)
  [s[0]-1,s[1]]  
end

def find_piece(hashset,mask,fb,piece)
  unless piece.include?(fb)
    piece << fb 
    mask[fb] = nil
  end
  tmp = neighbor(fb).find_all do |e|
    (hashset[e] == hashset[fb]) && mask[e]
  end
  tmp.each{|i| find_piece(hashset,mask,i,piece)}
end

def stat(hashset,piece)
  r = []
  centroid = []
  piece.each do |b|
    l = lower(b)
    if (hashset[l] && (hashset[l] != hashset[b])) || (l[0] == -1)
      r << b[1]
    end
    centroid << Rational(1,2) + b[1]
  end
  c = centroid.inject(:+)/piece.size
  {:xl=>r.min, :xr=>r.max+1, :cent=>c}
end

def stable?(h)
  h[:xl] < h[:cent] and h[:cent] < h[:xr]
end

def is_stable?(a)
  base = a[0]
  xl,xr = base[:xl],base[:xr]
  c = a.inject(0){|r,i| r+i[:cent]}/a.size
  h = {:xl=>xl, :xr=>xr, :cent=>c}
  stable?(h)
end

def search(hashset,mask,fb)
  piece = []
  find_piece(hashset,mask,fb,piece)
  attr = stat(hashset,piece)
  attrs = [attr]
  piece.each do |e|
    u = upper(e)
    next unless mask[u]
    unless hashset[u] == hashset[e]
      attrs << search(hashset,mask,u)
    end
  end
  attrs.flatten!
  raise "UNSTABLE" unless is_stable?(attrs)
  attrs
end

def trans(dataset)
  hashset = {}
  dataset.each_with_index do |m,i|
    m.each_with_index do |n,j|
      hashset[[i,j]] = n
    end
  end
  hashset
end

def diag(w,h,dataset)
  hashset = trans(dataset)
  mask = hashset.dup
  first_block = hashset.find{|i| i[0][0] == 0 && i[1]}[0]
  begin
    search(hashset,mask,first_block)
  rescue => evar
    raise unless evar.to_s == "UNSTABLE"
    puts evar
  else
    puts "STABLE"
  end
end

def main
  lines = File.open('input.txt').readlines.map!{|i| i.gsub(/\s/,'').split(//)}
  input = lines.map do |i|
    i.map do |j|
      if j=="." then nil else Integer(j) end
    end
  end

  while !input.empty?
    w,h = input.shift
    dataset = input.shift(Integer(h)).reverse!
    exit if w == 0 and h == 0
#    puts "width,height = #{[w,h]}\n"
#    dataset.each{|l| p l.map{|e| if e then e else 0 end}}
    diag(w,h,dataset)
  end
end

main