-- 压缩函数
function rleCompress(str)
  local result = {}
  local i = 1
  while i <= #str do
    local char = str:sub(i, i)
    local count = 1
    while i + count <= #str and str:sub(i + count, i + count) == char do
      count = count + 1
    end
    if count > 2 then
      table.insert(result, ("[%d]%s"):format(count, char))
    else
      table.insert(result, char:rep(count))
    end
    i = i + count
  end
  return table.concat(result)
end

-- 解压函数
function rleDecompress(str)
  local result = {}
  local i = 1
  while i <= #str do
    if str:sub(i, i) == "[" then
      local j = str:find("]", i)
      local num = tonumber(str:sub(i+1, j-1))
      local char = str:sub(j+1, j+1)
      table.insert(result, char:rep(num))
      i = j + 2
    else
      table.insert(result, str:sub(i, i))
      i = i + 1
    end
  end
  return table.concat(result)
end

-- 测试
file = fs.open("1.bimg","r")
original = file.readAll()
file.close()


local compressed = rleCompress(original)
print("原始:", original)
print("压缩:", compressed)
print("解压:", rleDecompress(compressed))
file = fs.open("12.bimg","w")
file.write(compressed)
file.close()