https://paiza.jp/logic_summoner/challenges/logics_skill_4005

logics_skill_4005.rb

# https://paiza.jp/logic_summoner/challenges/logics_skill_4005

def mark(board, table, w, max, color, base, ind)
  return if table[ind]
  return unless color == board[ind]
  r = ind % w
  table[ind] = base
  mark(board, table, w, max, color, base, ind - 1) if r > 0     # left
  mark(board, table, w, max, color, base, ind + 1) if r < w - 1 # right
  mark(board, table, w, max, color, base, ind - w) if ind >= w  # up
  mark(board, table, w, max, color, base, ind + w) if ind + w <= max # down
end

def wipe(board, table, w, max, color, base, ind)
  return unless board[ind] == color
  return unless table[ind] == base
  board[ind] = nil
  r = ind % w
  wipe(board, table, w, max, color, base, ind - 1) if r > 0     # left
  wipe(board, table, w, max, color, base, ind + 1) if r < w - 1 # right
  wipe(board, table, w, max, color, base, ind - w) if ind >= w  # up
  wipe(board, table, w, max, color, base, ind + w) if ind + w <= max # down
end

def fall(board, w, max, ind)
  return unless board[ind]
  target = ind + w
  loop do
    break if target > max
    break if board[target]
    board[target] = board[ind]
    board[ind] = nil
    target += w
    ind += w
  end
end

# main
w, h, spell = gets.split(' ').map(&:to_i)
board = h.times.map{ gets.chomp.chars }.flatten
max = w*h-1

ans = []
loop do
  table = []
  board.each.with_index do |c, i|
    next unless c
    mark(board, table, w, max, c, i, i)
  end
  point, size = table.compact.sort.chunk_while{|l, r| l == r}.map{|l| [l.first, l.size]}.max_by(&:last)
  break if size <= 1
  ans << point
  break if ans.size >= spell
  wipe(board, table, w, max, board[point], point, point)
  (max-w).downto(0){|i| fall(board, w, max, i) }
end

puts ans.size
ans.each do |n|
  puts "#{n % w + 1} #{n/w + 1}"
end